Why iOS APNS VOIP development(sandbox) push notification is not working?

I can imagine most of the application back-end servers are leveraging AWS SNS to send push notifications to android and iOS devices for it integrated well with FCM and APNS.

One day, I found my development iOS app is not receiving VOIP push notification anymore! This is extremely scaring for those who are providing real time service like call, messaging, streaming,…etc. After immediately testing our production app and confirmed this is a ‘development-only’ issue, I got some relief.