The iOS certificate for the app was revoked, preventing the delivery of notifications.
The root cause was found to be that two applications had been autoconfigured with the same Apple App ID, leading to the revocation of any existing APNs certificates for the same Apple App ID during Auto Configuration.
To resolve this issue, the client should use manual configuration when configuring iOS platforms for different apps with the same App ID. The client can follow the iOS Platform Configuration guide for manual certificate renewal processes.
Alternatively, the client may consider using Token-based Configuration, which offers a stateless way to communicate with APNs. This method has several advantages, including faster communication than certificate-based communication, the ability to use one token to distribute notifications for multiple apps, and no need for periodic certificate renewal. However, the token can be revoked or reissued at any time if required.