Server-to-Server notification not triggering?

I've provided a url in the app information section to get app store server to server notification on non-renewing subscription purchases. But I'm not getting any response from app store even after trying 4-5 test purchases using sandbox account in my device. Any help would be appreciated.

On checking this News and Updates they've cleared that now it's possible to get server to server notification on all in-app purchases.
Server-to-Server notification not triggering?
 
 
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