Unhandled Exception: MissingPluginException(No implementation found for method flutterToWatch on channel it.example.watch)

I am using awesome_notifications library, and to prevent, for example, MissingPluginException(No implementation found for method getAll on channel plugins.flutter.io/shared_preferences) it uses in AppDelegate:

SwiftAwesomeNotificationsPlugin.setPluginRegistrantCallback { registry in
          SwiftAwesomeNotificationsPlugin.register(
            with: registry.registrar(forPlugin: "io.flutter.plugins.awesomenotifications.AwesomeNotificationsPlugin")!)          
          FLTSharedPreferencesPlugin.register(
            with: registry.registrar(forPlugin: "io.flutter.plugins.sharedpreferences.SharedPreferencesPlugin")!)
      }

But I still have error with my custom channel: Unhandled Exception: MissingPluginException(No implementation found for method flutterToWatch on channel it.example.watch) And I don't know how to register it in the background like awesome_notifications do it.

My channel:

private func initFlutterChannel() {
        if let controller = window?.rootViewController as? FlutterViewController {
            let channel = FlutterMethodChannel(
                name: "it.example.watch",
                binaryMessenger: controller.binaryMessenger)
            
            channel.setMethodCallHandler({ [weak self] (
                call: FlutterMethodCall,
                result: @escaping FlutterResult) -> Void in
                switch call.method {
                case "flutterToWatch":
                    guard let watchSession = self?.session, watchSession.isPaired, watchSession.isReachable, let methodData = call.arguments as? [String: Any], let method = methodData["method"], let data = methodData["data"] else {
                                            result(false)
                                            return
                                        }
                    
                    let watchData: [String: Any] = ["method": method, "data": data]
                    
                    // Pass the receiving message to Apple Watch
                    watchSession.sendMessage(watchData, replyHandler: nil, errorHandler: nil)
                    result(true)
                default:
                    result(FlutterMethodNotImplemented)
                }
            })
        }
    }