Flutter Local Notification is not working on the real device (Android)

I am building an Android application using Flutter. My app needs to display local notification. I am using this package, https://pub.dev/packages/flutter_local_notifications. When I show the notification on the emulator it is working. But it is not working, when I compiled release APK and installed it on the actual device.

This is NotificationService class

import 'package:flutter_local_notifications/flutter_local_notifications.dart';

class NotificationService
{
  static FlutterLocalNotificationsPlugin? flip;

  static FlutterLocalNotificationsPlugin getFlipInstance()
  {
    if (flip == null) {
      flip = FlutterLocalNotificationsPlugin();

      // app_icon needs to be a added as a drawable
      // resource to the Android head project.
      var android = const AndroidInitializationSettings('@mipmap/ic_launcher');
      var ios = const IOSInitializationSettings();

      var settings = InitializationSettings(android: android, iOS: ios);
      flip!.initialize(settings);
    }

    return flip as FlutterLocalNotificationsPlugin;
  }


  static Future showNotification(String title, String body) async {
    var androidPlatformChannelSpecifics = const AndroidNotificationDetails("your channel id", "my channel name");
    var iOSPlatformChannelSpecifics = const IOSNotificationDetails();

    // initialise channel platform for both Android and iOS device.
    var platformChannelSpecifics = NotificationDetails(android: androidPlatformChannelSpecifics, iOS: iOSPlatformChannelSpecifics);

    await getFlipInstance().show(0, title,
        body,
        platformChannelSpecifics, payload: 'Default_Sound'
    );
  }
}

I show notification like this in the initState method of home page.

@override
  void initState() {
    super.initState();
    setState(() {
    NotificationService.showNotification("Local Notification", "Local Notification Message");
  }

As I mentioned, it works on the emulator. But when I generated an APK and installed it on the real device, it is not working.