Flutter workmanager error Domain=BGTaskSchedulerErrorDomain Code=3 "(null)" on iOS

Question

i'm trying to use workermanger with flutter about background service on ios. So this is my plist

Now this is my AppDelegate on xcode:

 import UIKit
import Flutter
import workmanager


    @UIApplicationMain
    @objc class AppDelegate: FlutterAppDelegate {
        
    override func userNotificationCenter(_ center: UNUserNotificationCenter,
                                            willPresent notification: UNNotification,
                                            withCompletionHandler completionHandler: @escaping (UNNotificationPresentationOptions) -> Void) {
            completionHandler(.alert) // shows banner even if app is in foreground
        }
        
    
        override func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey : Any]? = nil) -> Bool {
            WorkmanagerPlugin.registerTask(withIdentifier: "simpleTask")
            UIApplication.shared.setMinimumBackgroundFetchInterval(TimeInterval(60*15))
            GeneratedPluginRegistrant.register(with: self)
            return super.application(application, didFinishLaunchingWithOptions: launchOptions)
        }
    }

and now this is my Flutter code

import 'package:workmanager/workmanager.dart';

@pragma('vm:entry-point')
void callbackDispatcher() {
  Workmanager().executeTask((task, inputData) {
    switch (task) {
      case Workmanager.iOSBackgroundTask:
        print("The iOS background fetch was triggered");
        break;
    }
    bool success = true;
    return Future.value(success);
  });
}
void main() {
    WidgetsFlutterBinding.ensureInitialized();
   Workmanager().initialize(
    callbackDispatcher, // The top level function, aka callbackDispatcher
    isInDebugMode: true // If enabled it will post a notification whenever the task is running. Handy for debugging tasks
  );
  Workmanager().registerOneOffTask("simpleTask", "simpleTask");
  // Workmanager().registerPeriodicTask("simpleTask", "simpleTask");
  runApp(const MyApp());  
}

The error i receive is this:

Could not schedule app refresh: Error Domain=BGTaskSchedulerErrorDomain Code=3 "(null)"

can you suggest me where i'm lost? Maybe about the documentation, i can't understand i ask help to you.