The AuctionCheckoutComplete platform notification is sent for only 1 item's transaction when checkout is completed for an order.
It is not sent for all of the items purchased in an order.
When a buyer completes checkout for a combined payment, and the seller is subscribed to platform notifications for the AuctionCheckoutComplete notification, the notification is generated and delivered for only 1 of the items purchased in the order.
The item for which the notification is generated is the first item that was purchased in the order.
The notification is not generated for the other items purchased in the order.
Applications that receive this notification will get a GetItemTransactionsResponse payload with the ContainingOrder container that has the OrderID.
Here is an XML snippet showing what this looks like:
Upon receiving this notification, the application can make a GetOrders call to get the complete information for the order.
Here is an example using the OrderID in the XML snippet above:
<?xml version='1.0' encoding='utf-8'?>
NOTE. If ContainingOrder container is not getting returned in this notificaiton, please make sure to set the PayloadVersion to the latest supported Trading API version via SetNotificationPreferences as dosumented in this KB https://ebaydts.com/eBayKBDetails?KBid=1984.