Fix: Turning the bind of the ShippingMethodManagerInterface to a singleton, so that it can actually resolve the shipping methods

src/Shipping/Carriers/Elta/EltaFulfillmentService.php

@@ -278,6 +278,13 @@ class EltaFulfillmentService implements CarrierFulfillmentInterface, IssuesVouch
 
     public function trackShipment(Shipment $shipment): Collection
     {
+        // ELTA tracks a multi-parcel send by its main voucher only — an
+        // extra parcel's own number is rejected ("Λάθος ΣΥΔΕΤΑ"). Its
+        // history is the main voucher's, which is tracked on its own row.
+        if (! $shipment->is($this->masterOf($shipment))) {
+            return collect();
+        }
+
         $response = $this->client->getTracking([
             'web_vg' => $shipment->tracking_reference,
             'pel_code' => config('elta.apost_code'),