iOS 12 voip notifications not receiving

Voip notifications are received in iOS 13 and 14 versions but not receiving only in iOS 12 version devices.

For below iOS 13 versions, i have used voip notifications for both messages and calls since there are no restrictions to show callkit immediately when payload is received under iOS 13 versions. This is not creating any issue when uploaded to testflight from XCODE 11. When i use XCODE 12 and upload to testflight, voip notifications are not received only in iOS 12 version devices. Have anyone faced the same kind of issue?
I have been having this issue as a user after iOS 14.5

both robokiller app and callhero app are supposed to display the call notifications after screening the call to make sure its an actual person but my phone never rings, all I get is a silent notification saying to tap to open the app. strange thing is the developers of said app say they dont know of any issue like this as no one else is reporting this problem.

I even did a factory reset on my phone and setup as new and same thing, im missing all my calls.
iOS 12 voip notifications not receiving
 
 
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