IOS developers they have to upload Production Certificate obtained from IOS developer page. The file for the certificate should have p12 file extension. This certificate needs to be renewed every year.

Production certificate is created when the developer creates IOS certificate.

In iOS 8 and later, voice-over-IP (VoIP) apps register for UIRemoteNotificationTypeVoIP push notifications instead of using this method. Using push notifications eliminates the need for a timeout handler to check in with the VoIP community. 

Instead, when a calls arrives for the user, the VoIP community sends a VoIP push notification to the user’s device. Upon receiving this notification, the device launches or wakes the app as needed so that it can handle the incoming call.

VOIP certificate along with its password can also be created in IOS developer page. The file of this certificate needs to have p12 file extension and it needs to be renewed annually.