Some background first…
This is a user-to-user forum, not Apple.
The people that do work for Apple may or may not read postings here, and seldom reply.
This also isn’t the Apple Developer forums, as APNs are more commonly associated with and created by third-party app developers. There are rather fewer developers active in these forums too, as compared with the activity over in the developer forums.
Now for the APNs info:
Establishing a certificate-based connection to APNs | Apple Developer Documentation
Notifications Overview - Apple Developer
This might help with checking for a current APNs certificate and revoking any existing one:
https://howto.im/q/how-to-revoke-an-apple-push-notification-service-certificate