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We get a success response to the CompleteSales request as below, but the ShipmentTrackingNumber specified in the request is not reflected in GetItemTransactions for the transaction in question. What is the problem?
The possible cause of the issue might be:
As documented : before you can call CompleteSale, an item that you created as a buyer must have gone through a sale (thus creating a transaction) and pay the item. Use GetItemTransactions or GetSellerTransactions to retrieve a list of the transactions that have checkedout as: <CheckoutStatus>CheckoutComplete</CheckoutStatus>.