FIRInstanceID token null thel first time app starts, OK the second time

Question

I am implementing Firebase push notifications on my iOS app.

On didFinishLaunchingWithOptions, I call [FIRApp configure]. It returns nill token the first time the app starts, but if I run the app again, it returns a valid working token.

 NSString *refreshedToken = [[FIRInstanceID instanceID] token];

null the first time.

Here's the code in application didFinishLaunchingWithOptions::

- (void)handleFCMregister
{
    if (floor(NSFoundationVersionNumber) <= NSFoundationVersionNumber_iOS_9_x_Max) {
        UIUserNotificationType allNotificationTypes =
        (UIUserNotificationTypeSound | UIUserNotificationTypeAlert | UIUserNotificationTypeBadge);
        UIUserNotificationSettings *settings =
        [UIUserNotificationSettings settingsForTypes:allNotificationTypes categories:nil];
        [[UIApplication sharedApplication] registerUserNotificationSettings:settings];
    } else {
        // iOS 10 or later
#if defined(__IPHONE_10_0) && __IPHONE_OS_VERSION_MAX_ALLOWED >= __IPHONE_10_0
        UNAuthorizationOptions authOptions =
        UNAuthorizationOptionAlert
        | UNAuthorizationOptionSound
        | UNAuthorizationOptionBadge;
        [[UNUserNotificationCenter currentNotificationCenter]
         requestAuthorizationWithOptions:authOptions
         completionHandler:^(BOOL granted, NSError * _Nullable error) {
         }
         ];

        // For iOS 10 display notification (sent via APNS)
        [[UNUserNotificationCenter currentNotificationCenter] setDelegate:self];
        // For iOS 10 data message (sent via FCM)
        [[FIRMessaging messaging] setRemoteMessageDelegate:self];
#endif
    }

    [[UIApplication sharedApplication] registerForRemoteNotifications];

    [FIRApp configure];

    NSString *refreshedToken = [[FIRInstanceID instanceID] token];        
    DLog(@"refreshedToken ::%@", refreshedToken);
}

How to get a valid token the first time the app starts? What seems to be wrong? Thanks.