Not receiving an incoming call when app is running in background

Question

Not receiving an incoming call when app is in background(iOS and Android). we are using asure communication service to create a communication channel. The event is not triggered.

iOS

func pushRegistry(_ registry: PKPushRegistry, didReceiveIncomingPushWith payload: PKPushPayload, for type: PKPushType) {
        print(payload) 
        let callNotification = PushNotificationInfo.fromDictionary(payload.dictionaryPayload) 

        callAgent?.handlePush(notification: callNotification) { (error) in 
            if (error == nil) { 
                print("Handling of push notification was successful") 
            } else { 
                print("Handling of push notification failed") 
            } 
        }