Linphone background incoming calls VoIP push notifications -swift

Hi,
I have an application based on linphone for making voip calls,
Calling is working fine when app is in foreground, but we need to implement calling when app is in background or phone is locked.
Push notifications are enabled through voip pushkit and server sends push but the app crashes on incoming call if the phone is locked.

Please bid only if you have experience with push kit/voip

Thanks.