In iOS 13, an application that receives a PushKit VoIP push must report an incoming call to CallKit as announced in https://developer.apple.com/videos/play/wwdc2019/707/ and https://developer.apple.com/documentation/pushkit/pkpushregistrydelegate/2875784-pushregistryHowever, as you know, apps cannot use CallKit for users in Mainland China since 2018. How should a VoIP app handle receiving a PushKit VoIP push for a user in Mainland China?