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What is the order/flow in which I will recieive platform notifications?
Although this will only cover a few specific notifications, it will give the overall flow and order for transactional platform notifications.
There are two routes buyers can take, they can add items to their cart or "commit" to the buy on the item page. Each method yields a different flow.
1.Buyer uses the "commit" button
-Once a buyer "commits" to the purchase of an item by pressing the commit button, the seller will receive ItemSold and FixedPriceTransaction (for fixed price items) or EndOfAuction (for auction items) notifications. After the buyer completes checkout of the item the seller will receive the AuctionCheckoutComplete notification.
2.Buyers uses cart
-Once buyers add items to their cart, they must complete checkout before you receive any of the transactional notifications. Once checkout is completed, the seller will receive the ItemSold, FixedPriceTransation or EndOfAuction, and AuctionCheckoutComplete notifications.
Note - The AuctionCheckoutComplete platform notification is sent for only one item's transaction when checkout is completed for an order.
It is not sent for all of the items purchased in an 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.
For the payload of each notification, refer to API Call Payloads for Notifications
GetNotificationPreferences - https://developer.ebay.com/DevZone/XML/docs/Reference/eBay/GetNotificationPreferences.html