Order tracking: every call to tracking-api returns 500 since 9.5.5.3 (missing `PayPal-Merchant-Id` header), then 422 on address/SKU comparison

diff -ruN orig/config/shared/process.yml live/config/shared/process.yml
--- a/config/shared/process.yml
+++ b/config/shared/process.yml
@@ -129,6 +129,7 @@
       - '@PsCheckout\Core\PayPal\ShippingTracking\Service\TrackingDatabaseHandler'
       - '@PsCheckout\Infrastructure\Repository\CountryRepository'
       - '@PsCheckout\Infrastructure\Repository\StateRepository'
+      - '@PsCheckout\Core\PayPal\Order\Provider\PayPalOrderProvider'
 
   # Shipping Tracking Processor
   PsCheckout\Core\PayPal\ShippingTracking\Processor\ShipmentProcessorInterface:
@@ -143,6 +144,7 @@
       - '@PsCheckout\Core\PayPal\ShippingTracking\Service\TrackingDatabaseHandler'
       - '@PsCheckout\Infrastructure\Repository\CountryRepository'
       - '@PsCheckout\Infrastructure\Repository\StateRepository'
+      - '@PsCheckout\Core\PayPal\Order\Provider\PayPalOrderProvider'
 
   # External Shipping Tracking Processor
   PsCheckout\Core\PayPal\ShippingTracking\Processor\ExternalShipmentProcessor:
diff -ruN orig/vendor/invertus/api/src/Http/Configuration/OrderShipmentTrackingConfigurationBuilder.php live/vendor/invertus/api/src/Http/Configuration/OrderShipmentTrackingConfigurationBuilder.php
--- a/vendor/invertus/api/src/Http/Configuration/OrderShipmentTrackingConfigurationBuilder.php
+++ b/vendor/invertus/api/src/Http/Configuration/OrderShipmentTrackingConfigurationBuilder.php
@@ -20,6 +20,7 @@
 
 namespace PsCheckout\Api\Http\Configuration;
 
+use PsCheckout\Core\Settings\Configuration\PayPalConfiguration;
 use PsCheckout\Infrastructure\Adapter\ConfigurationInterface;
 use PsCheckout\Infrastructure\Adapter\LinkInterface;
 use PsCheckout\Infrastructure\Environment\EnvInterface;
@@ -78,6 +79,7 @@
                 'Checkout-Bn-Code' => $this->env->getBnCode(),
                 'Checkout-Module-Version' => $this->moduleVersion,
                 'Checkout-Prestashop-Version' => _PS_VERSION_,
+                'PayPal-Merchant-Id' => $this->configuration->get(PayPalConfiguration::PS_CHECKOUT_PAYPAL_ID_MERCHANT),
             ],
         ];
 
diff -ruN orig/vendor/invertus/core/src/PayPal/ShippingTracking/Builder/Node/TrackingItemsNodeBuilder.php live/vendor/invertus/core/src/PayPal/ShippingTracking/Builder/Node/TrackingItemsNodeBuilder.php
--- a/vendor/invertus/core/src/PayPal/ShippingTracking/Builder/Node/TrackingItemsNodeBuilder.php
+++ b/vendor/invertus/core/src/PayPal/ShippingTracking/Builder/Node/TrackingItemsNodeBuilder.php
@@ -139,11 +139,16 @@
      */
     private function resolveSku(array $product, array $productData): string
     {
+        // Prefer the order-line reference (= the SKU the PayPal order was created with), then the current product data.
+        if (!empty($product['reference'])) {
+            return $product['reference'];
+        }
+
         if (!empty($productData['sku'])) {
             return $productData['sku'];
         }
 
-        $sku = $product['reference'] ?? '';
+        $sku = '';
 
         if (empty($sku)) {
             $this->logger->warning('No SKU/reference found for product, sku field will be omitted from tracking payload.', [
diff -ruN orig/vendor/invertus/core/src/PayPal/ShippingTracking/Processor/ShipmentProcessor.php live/vendor/invertus/core/src/PayPal/ShippingTracking/Processor/ShipmentProcessor.php
--- a/vendor/invertus/core/src/PayPal/ShippingTracking/Processor/ShipmentProcessor.php
+++ b/vendor/invertus/core/src/PayPal/ShippingTracking/Processor/ShipmentProcessor.php
@@ -24,6 +24,7 @@
 use Order;
 use OrderCarrier;
 use OrderInvoice;
+use PsCheckout\Core\PayPal\Order\Provider\PayPalOrderProviderInterface;
 use PsCheckout\Core\PayPal\ShippingTracking\Builder\TrackingPayloadBuilderInterface;
 use PsCheckout\Core\PayPal\ShippingTracking\Cache\ShippingTrackingCacheInterface;
 use PsCheckout\Core\PayPal\ShippingTracking\Repository\ShippingTrackingRepositoryInterface;
@@ -87,6 +88,11 @@
      */
     private $stateRepository;
 
+    /**
+     * @var PayPalOrderProviderInterface
+     */
+    private $payPalOrderProvider;
+
     public function __construct(
         OrderTrackerValidatorInterface $orderTrackerValidator,
         TrackingPayloadBuilderInterface $payloadBuilder,
@@ -96,7 +102,8 @@
         TrackingApiService $trackingApiService,
         TrackingDatabaseHandler $trackingDatabaseHandler,
         CountryRepositoryInterface $countryRepository,
-        StateRepositoryInterface $stateRepository
+        StateRepositoryInterface $stateRepository,
+        PayPalOrderProviderInterface $payPalOrderProvider
     ) {
         $this->orderTrackerValidator = $orderTrackerValidator;
         $this->payloadBuilder = $payloadBuilder;
@@ -107,6 +114,7 @@
         $this->trackingDatabaseHandler = $trackingDatabaseHandler;
         $this->countryRepository = $countryRepository;
         $this->stateRepository = $stateRepository;
+        $this->payPalOrderProvider = $payPalOrderProvider;
     }
 
     /**
@@ -125,6 +133,10 @@
             $payPalOrder = $orderData['paypal_order'];
             $capture = $orderData['capture'];
 
+            // The tracking service compares the address node literally with the PayPal order's shipping address (which PayPal
+            // normalizes) and rejects a missing node with 422: send PayPal's own address when available.
+            $address = $this->getPayPalShippingAddress($payPalOrder->getId()) ?: $address;
+
             // Get products from order invoice
             $products = $this->getProductsFromOrderCarrier($orderCarrier);
 
@@ -235,7 +247,9 @@
                 $products[] = [
                     'id_product' => (int) $product['id_product'],
                     'id_product_attribute' => (int) ($product['product_attribute_id'] ?? 0),
-                    'reference' => $product['reference'] ?? '',
+                    // The SKU must be the one the PayPal order was created with, i.e. the reference stored on the order line
+                    // (order_detail.product_reference), not the current catalog reference.
+                    'reference' => !empty($product['product_reference']) ? $product['product_reference'] : ($product['reference'] ?? ''),
                     'quantity' => (int) $product['product_quantity'],
                     'name' => $product['product_name'] ?? '',
                 ];
@@ -287,6 +301,28 @@
         }
     }
 
+    /**
+     * Shipping address as PayPal knows it (from the cached provider: no API call when the COMPLETED order is already
+     * cached). Empty when unavailable: the PrestaShop delivery address is used as before.
+     *
+     * @param string $payPalOrderId
+     *
+     * @return array
+     */
+    private function getPayPalShippingAddress(string $payPalOrderId): array
+    {
+        try {
+            $purchaseUnits = $this->payPalOrderProvider->getById($payPalOrderId)->getPurchaseUnits();
+            $address = $purchaseUnits[0]['shipping']['address'] ?? [];
+
+            return is_array($address) ? array_filter($address, static function ($v) { return is_string($v) && $v !== ''; }) : [];
+        } catch (\Exception $e) {
+            $this->logger->warning('PayPal shipping address not available for order ' . $payPalOrderId . ': ' . $e->getMessage());
+
+            return [];
+        }
+    }
+
     /**
      * @param Order $order
      *

{"statusCode":500,"message":"Internal server error"}