Firebase Cloud Messaging (Flutter)：订阅主题时出现错误消息

我已经在我的应用程序中包含了Firebase消息，当我try 订阅主题时，我收到以下错误.

FLTFirebaseMessaging: An error occurred while calling method Messaging#subscribeToTopic, errorOrNil => {
    NSLocalizedFailureReason = "Invalid registration response :'Error=INVALID_PARAMETERS'. It is missing 'token' field.";
}
flutter: subscription error: [firebase_messaging/unknown] An unknown error has occurred.

正如您所看到的，它只是简单地说"发生了一个未知错误"，这对我来说没有太大帮助.

下面是我的代码，它旨在获取推送通知的权限，然后获取令牌并订阅主题列表……

  Future<void> requestMessagingPermission() async {
    FirebaseMessaging messaging = FirebaseMessaging.instance;

    NotificationSettings settings = await messaging.requestPermission(
      alert: true,
      announcement: false,
      badge: true,
      carPlay: false,
      criticalAlert: false,
      provisional: false,
      sound: true,
    );

    print('User granted permission: ${settings.authorizationStatus}');
    if (settings.authorizationStatus == AuthorizationStatus.authorized) {
      print('User granted notifiactions permission');
      messaging.getToken().then((token) async {
        print('Messaging token: $token');

        //configure notification topics
        //gets a list of strings (topic names) from provider and loops through them to subscribe to them all

        GlobalProvider provider = context.read<GlobalProvider>();
        if (provider.notificationTopicsSet == false) {
          //subscribe to topics
          for (var topic in provider.notificationTopics) {
            print('topic subscribing... $topic');
            try {
              await messaging.subscribeToTopic(topic).then((value) => print('topic subscribed: $topic'));
            } catch (e) {
              print('subscription error: $e');
            }
          }
        }
      });
    }
  }

我在控制台中收到的每个正在循环和订阅的主题都有相同的错误.奇怪的是，推送通知以前是有效的，但现在似乎不起作用了.

我已经try 将Ffltter更新到最新版本(3.3.7)，我已经try 将Firebase核心包(2.1.1)和Firebase消息传递包更新到它们的最新版本(14.0.4)，但我仍然收到错误.

From pubspec.yaml:个

  firebase_core: ^2.1.1
  firebase_messaging: ^14.0.4

这token个遗失的是什么？subscribeToTopic()函数似乎只接受主题名称字符串.我是不是遗漏了什么？

谢谢你，任何帮助都将不胜感激.