Firebase notifications not working in iOS 11

This is an issue with Firebase. It seems to be related to a recent update of theirs instead of iOS 11. They are working on a fix for it.

In the meantime if you add pod 'FirebaseInstanceID', '2.0.0' to your podfile it will fix it.

You can read more here: https://github.com/firebase/quickstart-ios/issues/327#issuecomment-332655731

Check this in your project capability. It's helped me)

You need to implement UNUserNotificationCenterDelegate

 extension AppDelegate: UNUserNotificationCenterDelegate {
        func userNotificationCenter(_ center: UNUserNotificationCenter, willPresent notification: UNNotification, withCompletionHandler completionHandler: @escaping (UNNotificationPresentationOptions) -> Void) {
            completionHandler(.alert)
        }
    }

and set it to UNUserNotificationCenter object inside didFinishLaunchingWithOptions

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
      UNUserNotificationCenter.current().delegate = self
      return true
}