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Question: I have subscribed to platform notifications, and I seem to be getting duplicate notifications. Why is this happening?
Answer: There are a couple of reasons why you could get duplicate notifications:
1. Multiple Apps with different keys, subscribe to the same notifications events for the same user and have the same ApplicationURL for delivering the notification. Although the urls are the same, since they are different applications eBay will deliver the notification for both the apps. The only difference in the notifications will be the notification signature. If you authenticate the signature, you will see that only some of the notifications match for your application.
2. When the eBay Notification Server sends a notification, it expects a response back with HTTP code 200 (OK) within 3 secs. If this is not received, the server will retry sending the notification.
If none of these are applicable in your case, you could file a support request with the details for further investigation.