Unable to connect with FCM. Optional(Error Domain=com.google.fcm Code=501

Solution: open push notification and in backgroud mode open remote notification in Xcode 8

iOS 9.3

// [START connect_to_fcm]

func connectToFcm() {

//FIRMessaging.messaging().connect { (error) in

FIRMessaging.messaging().connectWithCompletion { (error) in

if (error != nil) {

print(“Unable to connect with FCM. (error)”)

} else {

print(“Connected to FCM.”)

}

}

}
// [END connect_to_fcm]

func applicationDidBecomeActive(application: UIApplication) {

// Restart any tasks that were paused (or not yet started) while the application was inactive. If the application was previously in the background, optionally refresh the user interface.

connectToFcm() //add by Kevin

}