On the Amazon AppStore when a product is bought multiple times, OnPurchaseSucceeded is called instead of OnPurchaseFailed because a duplicate purchase is handled the same way as a normal purchase. See AmazonPurchasing.onPurchaseResponse

Reproduction steps (not tested):
Purchase the same product twice

Expected Behaviour: OnPurchaseSucceded callback should be triggered for the first purchase and the second purchase should fail and call the OnPurchaseFailed callback.

Actual Behaviour: OnPurchaseSucceded callback is called for both purchases.