diff --git a/src/Application/Order/CustomerResolverInterface.php b/src/Application/Order/CustomerResolverInterface.php
new file mode 100644
index 0000000..5c0e947
--- /dev/null
+++ b/src/Application/Order/CustomerResolverInterface.php
@@ -0,0 +1,26 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Application\Order;
+
+use App\Domain\Order\Customer;
+
+interface CustomerResolverInterface
+{
+    /**
+     * Finds or creates a Customer using a two-stage cascade:
+     * Stage 1: exact platform_id match (fast path)
+     * Stage 2: exact lowercase(name|street|city|zip) match (cross-platform dedup)
+     * No match: creates new customer in DB + Frappe ERP.
+     *
+     * @param array<string, string> $address  Keys: street, city, zip
+     */
+    public function resolve(
+        string $platform,
+        string $platformUserId,
+        string $name,
+        string $email,
+        array $address,
+    ): Customer;
+}
diff --git a/src/Application/Order/ErpAdapterInterface.php b/src/Application/Order/ErpAdapterInterface.php
new file mode 100644
index 0000000..2d69686
--- /dev/null
+++ b/src/Application/Order/ErpAdapterInterface.php
@@ -0,0 +1,29 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Application\Order;
+
+use App\Domain\Order\Customer;
+use App\Domain\Order\Order;
+
+interface ErpAdapterInterface
+{
+    /**
+     * Creates a Customer document in Frappe ERP.
+     * Returns the Frappe document name (e.g. "CUST-00001").
+     */
+    public function createCustomer(Customer $customer): string;
+
+    /**
+     * Creates and submits a Sales Invoice in Frappe ERP.
+     * Returns the Frappe document name (e.g. "SINV-00001").
+     */
+    public function createSalesInvoice(Order $order): string;
+
+    /**
+     * Fetches the PDF of a submitted Sales Invoice.
+     * Returns raw binary PDF content.
+     */
+    public function fetchInvoicePdf(string $frappeInvoiceId): string;
+}
diff --git a/src/Application/Order/InvoiceMailerInterface.php b/src/Application/Order/InvoiceMailerInterface.php
new file mode 100644
index 0000000..edd7511
--- /dev/null
+++ b/src/Application/Order/InvoiceMailerInterface.php
@@ -0,0 +1,16 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Application\Order;
+
+use App\Domain\Order\Invoice;
+
+interface InvoiceMailerInterface
+{
+    /**
+     * Sends the invoice PDF to the configured supplier email address.
+     * The supplier then ships the item (dropshipping model).
+     */
+    public function sendInvoice(Invoice $invoice): void;
+}
diff --git a/src/Infrastructure/Channel/Ebay/EbayAdapter.php b/src/Infrastructure/Channel/Ebay/EbayAdapter.php
new file mode 100644
index 0000000..5266234
--- /dev/null
+++ b/src/Infrastructure/Channel/Ebay/EbayAdapter.php
@@ -0,0 +1,126 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Infrastructure\Channel\Ebay;
+
+use App\Application\Channel\ChannelAdapterInterface;
+use App\Domain\Article\Article;
+use App\Domain\Article\ArticleCondition;
+use App\Domain\Order\Order;
+
+final class EbayAdapter implements ChannelAdapterInterface
+{
+    public function __construct(
+        private readonly EbayInventoryApiClient $apiClient,
+    ) {
+    }
+
+    public function getType(): string
+    {
+        return 'ebay';
+    }
+
+    public function publishListing(Article $article): string
+    {
+        $sku = $article->getSku();
+
+        $this->apiClient->upsertInventoryItem($sku, [
+            'availability' => [
+                'shipToLocationAvailability' => [
+                    'quantity' => $article->getStock(),
+                ],
+            ],
+            'condition' => $this->mapCondition($article->getCondition()),
+            'conditionDescription' => $article->getConditionNotes() ?? '',
+            'product' => [
+                'title' => $article->getEbayTitle() ?? $article->getSku(),
+                'description' => $article->getEbayDescription() ?? '',
+                'aspects' => $this->buildAspects($article),
+            ],
+        ]);
+
+        $offerId = $this->apiClient->createOffer([
+            'sku' => $sku,
+            'marketplaceId' => 'EBAY_DE',
+            'format' => 'FIXED_PRICE',
+            'availableQuantity' => $article->getStock(),
+            'pricingSummary' => [
+                'price' => [
+                    'currency' => 'EUR',
+                    'value' => number_format((float) ($article->getListingPrice() ?? '0'), 2, '.', ''),
+                ],
+            ],
+            'listingDescription' => $article->getEbayDescription() ?? '',
+            'categoryId' => $this->getCategoryId(),
+        ]);
+
+        return $this->apiClient->publishOffer($offerId);
+    }
+
+    public function updateStock(Article $article, int $stock): void
+    {
+        $this->apiClient->bulkUpdateInventoryItems([
+            'requests' => [
+                [
+                    'sku' => $article->getSku(),
+                    'shipToLocationAvailability' => [
+                        'quantity' => $stock,
+                    ],
+                ],
+            ],
+        ]);
+    }
+
+    public function deactivateListing(Article $article): void
+    {
+        $listingId = $article->getEbayListingId();
+        if (null === $listingId) {
+            return;
+        }
+
+        $this->apiClient->withdrawOffer($listingId);
+    }
+
+    public function pushTracking(Order $order): void
+    {
+        if (null === $order->getTrackingNumber()) {
+            throw new \RuntimeException('Order has no tracking number');
+        }
+
+        $this->apiClient->addTrackingToOrder($order->getPlatformOrderId(), [
+            'lineItems' => [
+                ['lineItemId' => $order->getPlatformOrderId(), 'quantity' => 1],
+            ],
+            'shippingCarrierCode' => $order->getCarrier() ?? 'DHL',
+            'trackingNumber' => $order->getTrackingNumber(),
+        ]);
+    }
+
+    private function mapCondition(ArticleCondition $condition): string
+    {
+        return match ($condition) {
+            ArticleCondition::New => 'NEW',
+            ArticleCondition::LikeNew => 'LIKE_NEW',
+            ArticleCondition::Good => 'GOOD',
+            ArticleCondition::Acceptable => 'ACCEPTABLE',
+        };
+    }
+
+    /** @return array<string, list<string>> */
+    private function buildAspects(Article $article): array
+    {
+        $aspects = [];
+        foreach ($article->getAttributeValues() as $value) {
+            $name = $value->getAttributeDefinition()->getName();
+            $aspects[$name] = [$value->getValue()];
+        }
+
+        return $aspects;
+    }
+
+    private function getCategoryId(): string
+    {
+        return '177';
+    }
+}
diff --git a/src/Infrastructure/Channel/Ebay/EbayFulfillmentApiClient.php b/src/Infrastructure/Channel/Ebay/EbayFulfillmentApiClient.php
new file mode 100644
index 0000000..8226bed
--- /dev/null
+++ b/src/Infrastructure/Channel/Ebay/EbayFulfillmentApiClient.php
@@ -0,0 +1,93 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Infrastructure\Channel\Ebay;
+
+use Symfony\Contracts\HttpClient\HttpClientInterface;
+
+final class EbayFulfillmentApiClient
+{
+    public function __construct(
+        private readonly EbayOAuthClient $oauthClient,
+        private readonly HttpClientInterface $httpClient,
+        private readonly string $apiBaseUrl,
+    ) {
+    }
+
+    /**
+     * Fetches a full order from eBay Sell Fulfillment API v1.
+     *
+     * Returns a normalized array with keys:
+     *   orderId, buyerUsername, buyerName, buyerEmail,
+     *   shippingStreet, shippingCity, shippingZip, shippingCountry,
+     *   ebayListingId, salePrice, saleDate
+     *
+     * @return array<string, string>
+     */
+    public function getOrder(string $orderId): array
+    {
+        $token = $this->oauthClient->getAccessToken();
+
+        $response = $this->httpClient->request(
+            'GET',
+            $this->apiBaseUrl.'/sell/fulfillment/v1/order/'.urlencode($orderId),
+            ['headers' => ['Authorization' => 'Bearer '.$token]],
+        );
+
+        /** @var array<string, mixed> $data */
+        $data = $response->toArray();
+
+        $ship = $this->nestedArray($data, 'fulfillmentStartInstructions', 0, 'shippingStep', 'shipTo');
+        $addr = $this->nestedArray($ship, 'contactAddress');
+        $line = $this->nestedArray($data, 'lineItems', 0);
+        $buyer = $this->nestedArray($data, 'buyer');
+        $buyerAddr = $this->nestedArray($buyer, 'buyerRegistrationAddress');
+        $total = $this->nestedArray($data, 'pricingSummary', 'total');
+
+        return [
+            'orderId' => $this->str($data['orderId'] ?? $orderId),
+            'buyerUsername' => $this->str($buyer['username'] ?? ''),
+            'buyerName' => $this->str($ship['fullName'] ?? $buyerAddr['fullName'] ?? ''),
+            'buyerEmail' => $this->str($ship['email'] ?? $buyerAddr['email'] ?? ($this->str($buyer['username'] ?? '').'@members.ebay.com')),
+            'shippingStreet' => $this->str($addr['addressLine1'] ?? ''),
+            'shippingCity' => $this->str($addr['city'] ?? ''),
+            'shippingZip' => $this->str($addr['postalCode'] ?? ''),
+            'shippingCountry' => $this->str($addr['countryCode'] ?? 'DE'),
+            'ebayListingId' => $this->str($line['legacyItemId'] ?? ''),
+            'salePrice' => $this->str($total['value'] ?? '0.00'),
+            'saleDate' => $this->str($data['creationDate'] ?? (new \DateTimeImmutable())->format(\DateTimeInterface::ATOM)),
+        ];
+    }
+
+    /**
+     * Safely retrieves a nested value from a mixed array using a variadic key path.
+     * Each key can be a string or int.
+     *
+     * @param array<string, mixed> $data
+     *
+     * @return array<string, mixed>
+     */
+    private function nestedArray(array $data, string|int ...$keys): array
+    {
+        $current = $data;
+        foreach ($keys as $key) {
+            if (!\array_key_exists($key, $current)) {
+                return [];
+            }
+            $val = $current[$key];
+            if (!\is_array($val)) {
+                return [];
+            }
+            $current = $val;
+        }
+
+        /** @var array<string, mixed> $current */
+        return $current;
+    }
+
+    private function str(mixed $value): string
+    {
+        return \is_scalar($value) ? (string) $value : '';
+    }
+}
diff --git a/src/Infrastructure/Channel/Ebay/EbayInventoryApiClient.php b/src/Infrastructure/Channel/Ebay/EbayInventoryApiClient.php
new file mode 100644
index 0000000..e667bc8
--- /dev/null
+++ b/src/Infrastructure/Channel/Ebay/EbayInventoryApiClient.php
@@ -0,0 +1,125 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Infrastructure\Channel\Ebay;
+
+use Symfony\Contracts\HttpClient\HttpClientInterface;
+
+class EbayInventoryApiClient
+{
+    private const INVENTORY_BASE = '/sell/inventory/v1';
+    private const FULFILLMENT_BASE = '/sell/fulfillment/v2';
+
+    public function __construct(
+        private readonly HttpClientInterface $httpClient,
+        private readonly EbayOAuthClient $oauthClient,
+        private readonly string $apiBaseUrl,
+        private readonly string $marketplaceId,
+    ) {
+    }
+
+    /**
+     * Creates or updates an inventory item (product + stock).
+     *
+     * @param array<string, mixed> $body
+     */
+    public function upsertInventoryItem(string $sku, array $body): void
+    {
+        $this->request('PUT', self::INVENTORY_BASE.'/inventory_item/'.urlencode($sku), $body);
+    }
+
+    /**
+     * Creates an offer (links inventory item to a listing).
+     *
+     * @param array<string, mixed> $body
+     *
+     * @return string offerId
+     */
+    public function createOffer(array $body): string
+    {
+        /** @var array{offerId: string} $response */
+        $response = $this->request('POST', self::INVENTORY_BASE.'/offer', $body);
+
+        return $response['offerId'];
+    }
+
+    /**
+     * Updates an existing offer.
+     *
+     * @param array<string, mixed> $body
+     */
+    public function updateOffer(string $offerId, array $body): void
+    {
+        $this->request('PUT', self::INVENTORY_BASE.'/offer/'.urlencode($offerId), $body);
+    }
+
+    /** @return string listingId */
+    public function publishOffer(string $offerId): string
+    {
+        /** @var array{listingId: string} $response */
+        $response = $this->request('POST', self::INVENTORY_BASE.'/offer/'.urlencode($offerId).'/publish', []);
+
+        return $response['listingId'];
+    }
+
+    public function withdrawOffer(string $offerId): void
+    {
+        $this->request('POST', self::INVENTORY_BASE.'/offer/'.urlencode($offerId).'/withdraw', []);
+    }
+
+    /** @param array<string, mixed> $quantityUpdate */
+    public function bulkUpdateInventoryItems(array $quantityUpdate): void
+    {
+        $this->request('POST', self::INVENTORY_BASE.'/bulk_update_price_quantity', $quantityUpdate);
+    }
+
+    /**
+     * Adds tracking info to an order.
+     *
+     * @param array<string, mixed> $body
+     */
+    public function addTrackingToOrder(string $orderId, array $body): void
+    {
+        $this->request('POST', self::FULFILLMENT_BASE.'/order/'.urlencode($orderId).'/shipping_fulfillment', $body);
+    }
+
+    /**
+     * @param array<string, mixed> $body
+     *
+     * @return array<string, mixed>
+     */
+    private function request(string $method, string $path, array $body): array
+    {
+        $token = $this->oauthClient->getAccessToken();
+
+        $options = [
+            'headers' => [
+                'Authorization' => 'Bearer '.$token,
+                'Content-Type' => 'application/json',
+                'X-EBAY-C-MARKETPLACE-ID' => $this->marketplaceId,
+            ],
+        ];
+
+        if ([] !== $body) {
+            $options['json'] = $body;
+        }
+
+        $response = $this->httpClient->request($method, $this->apiBaseUrl.$path, $options);
+
+        $statusCode = $response->getStatusCode();
+        if ($statusCode >= 400) {
+            $content = $response->getContent(false);
+            throw new \RuntimeException("eBay API error {$statusCode}: {$content}");
+        }
+
+        if (204 === $statusCode || '' === $response->getContent(false)) {
+            return [];
+        }
+
+        /** @var array<string, mixed> $data */
+        $data = $response->toArray();
+
+        return $data;
+    }
+}
diff --git a/src/Infrastructure/Channel/Ebay/EbayOAuthClient.php b/src/Infrastructure/Channel/Ebay/EbayOAuthClient.php
new file mode 100644
index 0000000..c5b559f
--- /dev/null
+++ b/src/Infrastructure/Channel/Ebay/EbayOAuthClient.php
@@ -0,0 +1,45 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Infrastructure\Channel\Ebay;
+
+use Symfony\Contracts\Cache\CacheInterface;
+use Symfony\Contracts\Cache\ItemInterface;
+use Symfony\Contracts\HttpClient\HttpClientInterface;
+
+final class EbayOAuthClient
+{
+    private const TOKEN_CACHE_KEY = 'ebay_access_token';
+
+    public function __construct(
+        private readonly HttpClientInterface $httpClient,
+        private readonly CacheInterface $cache,
+        private readonly string $clientId,
+        private readonly string $clientSecret,
+        private readonly string $oauthBaseUrl,
+    ) {
+    }
+
+    public function getAccessToken(): string
+    {
+        return $this->cache->get(self::TOKEN_CACHE_KEY, function (ItemInterface $item): string {
+            $credentials = base64_encode($this->clientId.':'.$this->clientSecret);
+
+            $response = $this->httpClient->request('POST', $this->oauthBaseUrl.'/identity/v1/oauth2/token', [
+                'headers' => [
+                    'Authorization' => 'Basic '.$credentials,
+                    'Content-Type' => 'application/x-www-form-urlencoded',
+                ],
+                'body' => 'grant_type=client_credentials&scope=https%3A%2F%2Fapi.ebay.com%2Foauth%2Fapi_scope',
+            ]);
+
+            /** @var array{access_token: string, expires_in: int} $data */
+            $data = $response->toArray();
+
+            $item->expiresAfter((int) ($data['expires_in'] * 0.8));
+
+            return $data['access_token'];
+        });
+    }
+}
diff --git a/src/Infrastructure/Channel/Ebay/EbayTaxonomyService.php b/src/Infrastructure/Channel/Ebay/EbayTaxonomyService.php
new file mode 100644
index 0000000..1640b18
--- /dev/null
+++ b/src/Infrastructure/Channel/Ebay/EbayTaxonomyService.php
@@ -0,0 +1,73 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Infrastructure\Channel\Ebay;
+
+use Symfony\Contracts\Cache\CacheInterface;
+use Symfony\Contracts\Cache\ItemInterface;
+use Symfony\Contracts\HttpClient\HttpClientInterface;
+
+final class EbayTaxonomyService
+{
+    public function __construct(
+        private readonly HttpClientInterface $httpClient,
+        private readonly EbayOAuthClient $oauthClient,
+        private readonly CacheInterface $cache,
+        private readonly string $apiBaseUrl,
+        private readonly string $marketplaceId,
+    ) {
+    }
+
+    /**
+     * Returns the required item aspect names for a given eBay category.
+     *
+     * @return list<array{name: string, required: bool, values: list<string>}>
+     */
+    public function getCategoryAspects(string $categoryId): array
+    {
+        $cacheKey = 'ebay_aspects_'.md5($this->marketplaceId.$categoryId);
+
+        return $this->cache->get($cacheKey, function (ItemInterface $item) use ($categoryId): array {
+            $item->expiresAfter(86400 * 7);
+
+            $token = $this->oauthClient->getAccessToken();
+
+            $response = $this->httpClient->request(
+                'GET',
+                $this->apiBaseUrl.'/commerce/taxonomy/v1/category_tree/'.$this->getTreeId().'/get_item_aspects_for_category',
+                [
+                    'headers' => [
+                        'Authorization' => 'Bearer '.$token,
+                        'X-EBAY-C-MARKETPLACE-ID' => $this->marketplaceId,
+                    ],
+                    'query' => ['category_id' => $categoryId],
+                ],
+            );
+
+            /** @var array{aspects?: list<array{localizedAspectName: string, aspectConstraint?: array{aspectRequired?: bool}, aspectValues?: list<array{localizedValue: string}>}>} $data */
+            $data = $response->toArray();
+            $aspects = [];
+
+            foreach ($data['aspects'] ?? [] as $aspect) {
+                $aspects[] = [
+                    'name' => $aspect['localizedAspectName'],
+                    'required' => $aspect['aspectConstraint']['aspectRequired'] ?? false,
+                    'values' => array_column($aspect['aspectValues'] ?? [], 'localizedValue'),
+                ];
+            }
+
+            return $aspects;
+        });
+    }
+
+    private function getTreeId(): string
+    {
+        return match ($this->marketplaceId) {
+            'EBAY_DE' => '77',
+            'EBAY_US' => '0',
+            'EBAY_UK' => '3',
+            default => '77',
+        };
+    }
+}
diff --git a/src/Infrastructure/Channel/Ebay/EbayWebhookVerifier.php b/src/Infrastructure/Channel/Ebay/EbayWebhookVerifier.php
new file mode 100644
index 0000000..c524b30
--- /dev/null
+++ b/src/Infrastructure/Channel/Ebay/EbayWebhookVerifier.php
@@ -0,0 +1,36 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Infrastructure\Channel\Ebay;
+
+final class EbayWebhookVerifier
+{
+    public function __construct(
+        private readonly string $verificationToken,
+        private readonly string $endpointUrl,
+    ) {
+    }
+
+    /**
+     * Verifies the HMAC-SHA256 signature on an eBay webhook notification.
+     * eBay signature: base64(SHA256(requestBody + verificationToken + endpointUrl)).
+     */
+    public function verify(string $requestBody, string $signatureHeader): bool
+    {
+        $expected = base64_encode(
+            hash('sha256', $requestBody.$this->verificationToken.$this->endpointUrl, binary: true),
+        );
+
+        return hash_equals($expected, $signatureHeader);
+    }
+
+    /**
+     * Returns the expected challenge response for endpoint registration.
+     * eBay sends GET ?challenge_code=XXX — we respond with SHA256(code + token + url).
+     */
+    public function challengeResponse(string $challengeCode): string
+    {
+        return hash('sha256', $challengeCode.$this->verificationToken.$this->endpointUrl);
+    }
+}
diff --git a/src/Infrastructure/Channel/Frappe/FrappeErpAdapter.php b/src/Infrastructure/Channel/Frappe/FrappeErpAdapter.php
new file mode 100644
index 0000000..f65b86a
--- /dev/null
+++ b/src/Infrastructure/Channel/Frappe/FrappeErpAdapter.php
@@ -0,0 +1,82 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Infrastructure\Channel\Frappe;
+
+use App\Application\Order\ErpAdapterInterface;
+use App\Domain\Order\Customer;
+use App\Domain\Order\Order;
+
+final class FrappeErpAdapter implements ErpAdapterInterface
+{
+    public function __construct(
+        private readonly FrappeHttpClient $frappe,
+        private readonly string $genericItemCode,
+    ) {
+    }
+
+    public function createCustomer(Customer $customer): string
+    {
+        $data = [
+            'customer_name' => $customer->getName(),
+            'customer_type' => 'Individual',
+            'customer_group' => 'Individual',
+            'territory' => 'Germany',
+            'custom_superseller_customer_id' => $customer->getId()->toRfc4122(),
+        ];
+
+        $ebayUserId = $customer->getPlatformId('ebay');
+        if (null !== $ebayUserId) {
+            $data['custom_ebay_user_id'] = $ebayUserId;
+        }
+
+        $response = $this->frappe->post('/api/resource/Customer', $data);
+
+        /** @var array{data: array{name: string}} $response */
+        return $response['data']['name'];
+    }
+
+    public function createSalesInvoice(Order $order): string
+    {
+        $article = $order->getArticle();
+        $customer = $order->getCustomer();
+
+        $draft = $this->frappe->post('/api/resource/Sales Invoice', [
+            'customer' => $customer->getFrappeCustomerId(),
+            'posting_date' => $order->getSaleDate()->format('Y-m-d'),
+            'due_date' => $order->getSaleDate()->format('Y-m-d'),
+            'items' => [
+                [
+                    'item_code' => $this->genericItemCode,
+                    'item_name' => $article->getEbayTitle() ?? $article->getSku(),
+                    'description' => \sprintf('%s — Inventar: %s', $article->getEbayTitle() ?? $article->getSku(), $article->getInventoryNumber()),
+                    'qty' => 1,
+                    'rate' => $order->getSalePrice(),
+                ],
+            ],
+            'custom_platform_order_id' => $order->getPlatformOrderId(),
+            'custom_article_inventory_number' => $article->getInventoryNumber(),
+        ]);
+
+        /** @var array{data: array{name: string}} $draft */
+        $invoiceName = $draft['data']['name'];
+
+        $this->frappe->post('/api/resource/Sales Invoice/'.$invoiceName.'/submit', []);
+
+        return $invoiceName;
+    }
+
+    public function fetchInvoicePdf(string $frappeInvoiceId): string
+    {
+        $path = http_build_query([
+            'doctype' => 'Sales Invoice',
+            'name' => $frappeInvoiceId,
+            'format' => 'Standard',
+            'no_letterhead' => '0',
+            '_lang' => 'de',
+        ]);
+
+        return $this->frappe->getContent('/api/method/frappe.utils.print_format.download_pdf?'.$path);
+    }
+}
diff --git a/src/Infrastructure/Channel/Frappe/FrappeHttpClient.php b/src/Infrastructure/Channel/Frappe/FrappeHttpClient.php
new file mode 100644
index 0000000..01e0546
--- /dev/null
+++ b/src/Infrastructure/Channel/Frappe/FrappeHttpClient.php
@@ -0,0 +1,54 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Infrastructure\Channel\Frappe;
+
+use Symfony\Contracts\HttpClient\HttpClientInterface;
+
+class FrappeHttpClient
+{
+    private string $authHeader;
+
+    public function __construct(
+        private readonly HttpClientInterface $httpClient,
+        private readonly string $baseUrl,
+        string $apiKey,
+        string $apiSecret,
+    ) {
+        $this->authHeader = "token {$apiKey}:{$apiSecret}";
+    }
+
+    /**
+     * POST to a Frappe resource endpoint.
+     *
+     * @param array<string, mixed> $data
+     *
+     * @return array<string, mixed>
+     */
+    public function post(string $path, array $data): array
+    {
+        $response = $this->httpClient->request('POST', $this->baseUrl.$path, [
+            'headers' => [
+                'Authorization' => $this->authHeader,
+                'Content-Type' => 'application/json',
+            ],
+            'json' => $data,
+        ]);
+
+        /** @var array<string, mixed> $result */
+        $result = $response->toArray();
+
+        return $result;
+    }
+
+    /** GET raw binary content (for PDF downloads). */
+    public function getContent(string $path): string
+    {
+        $response = $this->httpClient->request('GET', $this->baseUrl.$path, [
+            'headers' => ['Authorization' => $this->authHeader],
+        ]);
+
+        return $response->getContent();
+    }
+}
diff --git a/src/Infrastructure/Http/Controller/Webhook/EbayWebhookController.php b/src/Infrastructure/Http/Controller/Webhook/EbayWebhookController.php
new file mode 100644
index 0000000..e342b24
--- /dev/null
+++ b/src/Infrastructure/Http/Controller/Webhook/EbayWebhookController.php
@@ -0,0 +1,100 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Infrastructure\Http\Controller\Webhook;
+
+use App\Infrastructure\Channel\Ebay\EbayWebhookVerifier;
+use App\Infrastructure\Messenger\Message\OrderReceivedMessage;
+use Psr\Log\LoggerInterface;
+use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;
+use Symfony\Component\HttpFoundation\JsonResponse;
+use Symfony\Component\HttpFoundation\Request;
+use Symfony\Component\HttpFoundation\Response;
+use Symfony\Component\Messenger\MessageBusInterface;
+use Symfony\Component\Routing\Attribute\Route;
+
+#[Route('/webhooks/ebay', name: 'webhook_ebay')]
+final class EbayWebhookController extends AbstractController
+{
+    public function __construct(
+        private readonly EbayWebhookVerifier $verifier,
+        private readonly MessageBusInterface $bus,
+        private readonly LoggerInterface $logger,
+    ) {
+    }
+
+    #[Route('', name: '_challenge', methods: ['GET'])]
+    public function challenge(Request $request): JsonResponse
+    {
+        $challengeCode = $request->query->getString('challenge_code');
+        if ('' === $challengeCode) {
+            return $this->json(['error' => 'Missing challenge_code'], Response::HTTP_BAD_REQUEST);
+        }
+
+        return $this->json(['challengeResponse' => $this->verifier->challengeResponse($challengeCode)]);
+    }
+
+    #[Route('', name: '_notify', methods: ['POST'])]
+    public function notify(Request $request): Response
+    {
+        $signature = $request->headers->get('X-EBAY-SIGNATURE', '');
+        $body = $request->getContent();
+
+        if (!$this->verifier->verify($body, $signature)) {
+            $this->logger->warning('eBay webhook: invalid signature', ['ip' => $request->getClientIp()]);
+
+            return new Response('', Response::HTTP_UNAUTHORIZED);
+        }
+
+        try {
+            /** @var array{notification?: array{topic?: string, data?: array<string, mixed>}} $payload */
+            $payload = json_decode($body, true, 512, \JSON_THROW_ON_ERROR);
+        } catch (\JsonException) {
+            return new Response('', Response::HTTP_BAD_REQUEST);
+        }
+
+        $topic = $payload['notification']['topic'] ?? '';
+        $data = $payload['notification']['data'] ?? [];
+
+        $this->logger->info('eBay webhook received', ['topic' => $topic]);
+
+        match ($topic) {
+            'FIXED_PRICE_TRANSACTION',
+            'AUCTION_CHECKOUT_COMPLETE' => $this->handleOrderEvent($data),
+            'MARKETPLACE_ACCOUNT_DELETION' => $this->handleAccountDeletion($data),
+            default => null,
+        };
+
+        return new Response('', Response::HTTP_OK);
+    }
+
+    /** @param array<string, mixed> $data */
+    private function handleOrderEvent(array $data): void
+    {
+        $rawOrderId = $data['orderId'] ?? null;
+        if (null === $rawOrderId) {
+            /** @var array<string, mixed> $orderData */
+            $orderData = \is_array($data['order'] ?? null) ? $data['order'] : [];
+            $rawOrderId = $orderData['orderId'] ?? '';
+        }
+        $orderId = \is_scalar($rawOrderId) ? (string) $rawOrderId : '';
+        if ('' === $orderId) {
+            $this->logger->error('eBay webhook: order event with no orderId', ['data' => $data]);
+
+            return;
+        }
+
+        $this->bus->dispatch(new OrderReceivedMessage(
+            platformOrderId: $orderId,
+            platformType: 'ebay',
+            rawPayload: $data,
+        ));
+    }
+
+    /** @param array<string, mixed> $data */
+    private function handleAccountDeletion(array $data): void
+    {
+        $this->logger->info('eBay MARKETPLACE_ACCOUNT_DELETION received', ['data' => $data]);
+    }
+}
diff --git a/src/Infrastructure/Mail/SymfonyInvoiceMailer.php b/src/Infrastructure/Mail/SymfonyInvoiceMailer.php
new file mode 100644
index 0000000..2081b08
--- /dev/null
+++ b/src/Infrastructure/Mail/SymfonyInvoiceMailer.php
@@ -0,0 +1,55 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Infrastructure\Mail;
+
+use App\Application\Order\InvoiceMailerInterface;
+use App\Domain\Order\Invoice;
+use Symfony\Component\Mailer\MailerInterface;
+use Symfony\Component\Mime\Email;
+
+final class SymfonyInvoiceMailer implements InvoiceMailerInterface
+{
+    public function __construct(
+        private readonly MailerInterface $mailer,
+        private readonly string $supplierEmail,
+        private readonly string $senderEmail,
+    ) {
+    }
+
+    public function sendInvoice(Invoice $invoice): void
+    {
+        $order = $invoice->getOrder();
+        $article = $order->getArticle();
+        $customer = $order->getCustomer();
+
+        $body = \sprintf(
+            "Neue Bestellung eingegangen — bitte sofort versenden.\n\n"
+            ."Bestellnummer : %s\n"
+            ."Artikel       : %s\n"
+            ."Inventarnummer: %s\n"
+            ."Käufer        : %s\n"
+            ."Verkaufspreis : €%s\n\n"
+            .'Die Rechnung liegt diesem E-Mail als PDF bei.',
+            $order->getPlatformOrderId(),
+            $article->getEbayTitle() ?? $article->getSku(),
+            $article->getInventoryNumber(),
+            $customer->getName(),
+            $order->getSalePrice(),
+        );
+
+        $email = (new Email())
+            ->from($this->senderEmail)
+            ->to($this->supplierEmail)
+            ->subject('Neue Bestellung: '.$order->getPlatformOrderId())
+            ->text($body)
+            ->attachFromPath(
+                $invoice->getFullPath(),
+                'Rechnung-'.$invoice->getFrappeInvoiceId().'.pdf',
+                'application/pdf',
+            );
+
+        $this->mailer->send($email);
+    }
+}
diff --git a/src/Infrastructure/Order/CustomerResolver.php b/src/Infrastructure/Order/CustomerResolver.php
new file mode 100644
index 0000000..3ece85c
--- /dev/null
+++ b/src/Infrastructure/Order/CustomerResolver.php
@@ -0,0 +1,51 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Infrastructure\Order;
+
+use App\Application\Order\CustomerResolverInterface;
+use App\Application\Order\ErpAdapterInterface;
+use App\Domain\Order\Customer;
+use App\Domain\Order\Repository\CustomerRepositoryInterface;
+
+final class CustomerResolver implements CustomerResolverInterface
+{
+    public function __construct(
+        private readonly CustomerRepositoryInterface $customers,
+        private readonly ErpAdapterInterface $erp,
+    ) {
+    }
+
+    public function resolve(
+        string $platform,
+        string $platformUserId,
+        string $name,
+        string $email,
+        array $address,
+    ): Customer {
+        $customer = $this->customers->findByPlatformId($platform, $platformUserId);
+        if (null !== $customer) {
+            return $customer;
+        }
+
+        $probe = new Customer($name, $email, $address);
+        $customer = $this->customers->findByMatchingKey($probe->getMatchingKey());
+        if (null !== $customer) {
+            $customer->addPlatformId($platform, $platformUserId);
+            $this->customers->save($customer);
+
+            return $customer;
+        }
+
+        $customer = new Customer($name, $email, $address);
+        $customer->addPlatformId($platform, $platformUserId);
+
+        $frappeId = $this->erp->createCustomer($customer);
+        $customer->setFrappeCustomerId($frappeId);
+
+        $this->customers->save($customer);
+
+        return $customer;
+    }
+}
diff --git a/tests/Unit/Infrastructure/Channel/Ebay/EbayAdapterTest.php b/tests/Unit/Infrastructure/Channel/Ebay/EbayAdapterTest.php
new file mode 100644
index 0000000..01b60e9
--- /dev/null
+++ b/tests/Unit/Infrastructure/Channel/Ebay/EbayAdapterTest.php
@@ -0,0 +1,61 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Tests\Unit\Infrastructure\Channel\Ebay;
+
+use App\Domain\Article\Article;
+use App\Domain\Article\ArticleCondition;
+use App\Domain\Article\ArticleType;
+use App\Infrastructure\Channel\Ebay\EbayAdapter;
+use App\Infrastructure\Channel\Ebay\EbayInventoryApiClient;
+use PHPUnit\Framework\MockObject\MockObject;
+use PHPUnit\Framework\TestCase;
+
+final class EbayAdapterTest extends TestCase
+{
+    private EbayInventoryApiClient&MockObject $apiClient;
+    private EbayAdapter $adapter;
+    private Article $article;
+
+    protected function setUp(): void
+    {
+        $this->apiClient = $this->createMock(EbayInventoryApiClient::class);
+        $this->adapter = new EbayAdapter($this->apiClient);
+        $this->article = new Article(new ArticleType('Notebook'), 'NB-001', 'INV-001', 1, ArticleCondition::Good);
+        $this->article->setEbayTitle('Dell Latitude 5520');
+        $this->article->setListingPrice('299.00');
+    }
+
+    public function test_get_type_returns_ebay(): void
+    {
+        $this->assertSame('ebay', $this->adapter->getType());
+    }
+
+    public function test_publish_listing_calls_upsert_create_and_publish(): void
+    {
+        $this->apiClient->expects($this->once())->method('upsertInventoryItem');
+        $this->apiClient->expects($this->once())->method('createOffer')->willReturn('offer-123');
+        $this->apiClient->expects($this->once())->method('publishOffer')->with('offer-123')->willReturn('listing-456');
+
+        $listingId = $this->adapter->publishListing($this->article);
+
+        $this->assertSame('listing-456', $listingId);
+    }
+
+    public function test_deactivate_listing_withdraws_offer(): void
+    {
+        $this->article->setEbayListingId('offer-123');
+
+        $this->apiClient->expects($this->once())->method('withdrawOffer')->with('offer-123');
+
+        $this->adapter->deactivateListing($this->article);
+    }
+
+    public function test_deactivate_listing_is_noop_when_no_listing_id(): void
+    {
+        $this->apiClient->expects($this->never())->method('withdrawOffer');
+
+        $this->adapter->deactivateListing($this->article);
+    }
+}
diff --git a/tests/Unit/Infrastructure/Channel/Ebay/EbayWebhookVerifierTest.php b/tests/Unit/Infrastructure/Channel/Ebay/EbayWebhookVerifierTest.php
new file mode 100644
index 0000000..1c716e9
--- /dev/null
+++ b/tests/Unit/Infrastructure/Channel/Ebay/EbayWebhookVerifierTest.php
@@ -0,0 +1,42 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Tests\Unit\Infrastructure\Channel\Ebay;
+
+use App\Infrastructure\Channel\Ebay\EbayWebhookVerifier;
+use PHPUnit\Framework\TestCase;
+
+final class EbayWebhookVerifierTest extends TestCase
+{
+    private EbayWebhookVerifier $verifier;
+
+    protected function setUp(): void
+    {
+        $this->verifier = new EbayWebhookVerifier(
+            verificationToken: 'my-secret-token',
+            endpointUrl: 'https://example.com/webhooks/ebay',
+        );
+    }
+
+    public function test_valid_signature_passes(): void
+    {
+        $body = '{"notification":{"data":{"orderId":"123"}}}';
+        $expected = base64_encode(hash('sha256', $body.'my-secret-tokenhttps://example.com/webhooks/ebay', binary: true));
+
+        $this->assertTrue($this->verifier->verify($body, $expected));
+    }
+
+    public function test_invalid_signature_fails(): void
+    {
+        $this->assertFalse($this->verifier->verify('{"body":"x"}', 'invalidsignature'));
+    }
+
+    public function test_challenge_response_returns_correct_hash(): void
+    {
+        $challengeCode = 'abc123';
+        $expected = hash('sha256', $challengeCode.'my-secret-tokenhttps://example.com/webhooks/ebay');
+
+        $this->assertSame($expected, $this->verifier->challengeResponse($challengeCode));
+    }
+}
diff --git a/tests/Unit/Infrastructure/Channel/Frappe/FrappeErpAdapterTest.php b/tests/Unit/Infrastructure/Channel/Frappe/FrappeErpAdapterTest.php
new file mode 100644
index 0000000..bef8d86
--- /dev/null
+++ b/tests/Unit/Infrastructure/Channel/Frappe/FrappeErpAdapterTest.php
@@ -0,0 +1,82 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Tests\Unit\Infrastructure\Channel\Frappe;
+
+use App\Domain\Article\Article;
+use App\Domain\Article\ArticleCondition;
+use App\Domain\Article\ArticleType;
+use App\Domain\Channel\Platform;
+use App\Domain\Order\Customer;
+use App\Domain\Order\Order;
+use App\Infrastructure\Channel\Frappe\FrappeErpAdapter;
+use App\Infrastructure\Channel\Frappe\FrappeHttpClient;
+use PHPUnit\Framework\MockObject\MockObject;
+use PHPUnit\Framework\TestCase;
+
+final class FrappeErpAdapterTest extends TestCase
+{
+    private FrappeHttpClient&MockObject $frappe;
+    private FrappeErpAdapter $adapter;
+
+    protected function setUp(): void
+    {
+        $this->frappe = $this->createMock(FrappeHttpClient::class);
+        $this->adapter = new FrappeErpAdapter($this->frappe, 'REFURB-HW');
+    }
+
+    public function test_create_customer_returns_frappe_id(): void
+    {
+        $this->frappe
+            ->method('post')
+            ->with('/api/resource/Customer', $this->isType('array'))
+            ->willReturn(['data' => ['name' => 'CUST-00001']]);
+
+        $customer = new Customer('Max Mustermann', 'max@test.de', ['street' => 'Str 1', 'city' => 'Berlin', 'zip' => '10115']);
+        $customer->addPlatformId('ebay', 'buyer123');
+
+        $result = $this->adapter->createCustomer($customer);
+
+        $this->assertSame('CUST-00001', $result);
+    }
+
+    public function test_create_sales_invoice_submits_and_returns_id(): void
+    {
+        $this->frappe
+            ->expects($this->exactly(2))
+            ->method('post')
+            ->willReturnOnConsecutiveCalls(
+                ['data' => ['name' => 'SINV-00001']],
+                ['data' => ['name' => 'SINV-00001', 'docstatus' => 1]],
+            );
+
+        $customer = new Customer('Max Mustermann', 'max@test.de', ['street' => 'Str 1', 'city' => 'Berlin', 'zip' => '10115']);
+        $customer->setFrappeCustomerId('CUST-00001');
+
+        $order = new Order(
+            new Article(new ArticleType('Laptop'), 'LAP-001', 'INV-001', 1, ArticleCondition::Good),
+            $customer,
+            new Platform('ebay', 'eBay DE'),
+            'ORDER-001',
+            '299.99',
+            new \DateTimeImmutable('2026-05-13'),
+        );
+
+        $result = $this->adapter->createSalesInvoice($order);
+
+        $this->assertSame('SINV-00001', $result);
+    }
+
+    public function test_fetch_invoice_pdf_returns_binary(): void
+    {
+        $this->frappe
+            ->method('getContent')
+            ->with($this->stringContains('SINV-00001'))
+            ->willReturn('%PDF-binary-content');
+
+        $result = $this->adapter->fetchInvoicePdf('SINV-00001');
+
+        $this->assertStringStartsWith('%PDF', $result);
+    }
+}
diff --git a/tests/Unit/Infrastructure/Order/CustomerResolverTest.php b/tests/Unit/Infrastructure/Order/CustomerResolverTest.php
new file mode 100644
index 0000000..2fff7bf
--- /dev/null
+++ b/tests/Unit/Infrastructure/Order/CustomerResolverTest.php
@@ -0,0 +1,89 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Tests\Unit\Infrastructure\Order;
+
+use App\Application\Order\ErpAdapterInterface;
+use App\Domain\Order\Customer;
+use App\Domain\Order\Repository\CustomerRepositoryInterface;
+use App\Infrastructure\Order\CustomerResolver;
+use PHPUnit\Framework\MockObject\MockObject;
+use PHPUnit\Framework\TestCase;
+
+final class CustomerResolverTest extends TestCase
+{
+    private CustomerRepositoryInterface&MockObject $customerRepo;
+    private ErpAdapterInterface&MockObject $erp;
+    private CustomerResolver $resolver;
+
+    protected function setUp(): void
+    {
+        $this->customerRepo = $this->createMock(CustomerRepositoryInterface::class);
+        $this->erp = $this->createMock(ErpAdapterInterface::class);
+        $this->resolver = new CustomerResolver($this->customerRepo, $this->erp);
+    }
+
+    public function test_stage_1_platform_id_match_returns_existing_customer_without_erp_call(): void
+    {
+        $existing = new Customer('Max Mustermann', 'max@test.de', ['street' => 'Musterstr 1', 'city' => 'Berlin', 'zip' => '10115']);
+        $existing->addPlatformId('ebay', 'buyer123');
+
+        $this->customerRepo
+            ->method('findByPlatformId')
+            ->with('ebay', 'buyer123')
+            ->willReturn($existing);
+
+        $this->erp->expects($this->never())->method('createCustomer');
+        $this->customerRepo->expects($this->never())->method('save');
+
+        $result = $this->resolver->resolve(
+            'ebay', 'buyer123',
+            'Max Mustermann', 'max@test.de',
+            ['street' => 'Musterstr 1', 'city' => 'Berlin', 'zip' => '10115'],
+        );
+
+        $this->assertSame($existing, $result);
+    }
+
+    public function test_stage_2_address_match_adds_platform_id_and_saves(): void
+    {
+        $existing = new Customer('Max Mustermann', 'max@test.de', ['street' => 'Musterstr 1', 'city' => 'Berlin', 'zip' => '10115']);
+
+        $this->customerRepo->method('findByPlatformId')->willReturn(null);
+        $this->customerRepo
+            ->method('findByMatchingKey')
+            ->with($existing->getMatchingKey())
+            ->willReturn($existing);
+        $this->customerRepo->expects($this->once())->method('save')->with($existing);
+
+        $this->erp->expects($this->never())->method('createCustomer');
+
+        $result = $this->resolver->resolve(
+            'ebay', 'buyer456',
+            'Max Mustermann', 'max@test.de',
+            ['street' => 'Musterstr 1', 'city' => 'Berlin', 'zip' => '10115'],
+        );
+
+        $this->assertSame($existing, $result);
+        $this->assertSame('buyer456', $result->getPlatformId('ebay'));
+    }
+
+    public function test_no_match_creates_new_customer_via_erp(): void
+    {
+        $this->customerRepo->method('findByPlatformId')->willReturn(null);
+        $this->customerRepo->method('findByMatchingKey')->willReturn(null);
+        $this->customerRepo->expects($this->once())->method('save');
+        $this->erp->method('createCustomer')->willReturn('CUST-99999');
+
+        $result = $this->resolver->resolve(
+            'ebay', 'newbuyer',
+            'Neue Käuferin', 'neu@test.de',
+            ['street' => 'Neustr 5', 'city' => 'München', 'zip' => '80333'],
+        );
+
+        $this->assertSame('CUST-99999', $result->getFrappeCustomerId());
+        $this->assertSame('newbuyer', $result->getPlatformId('ebay'));
+        $this->assertSame('Neue Käuferin', $result->getName());
+    }
+}