Unable to use Local Notifications plugin

Hello,
I am trying to use Local Notifications plugin in my project to push local notifications on the android device. But when I installed the plugin (https://ionicframework.com/docs/native/local-notifications/) and when I tried to build project for android platform I got following error .

/home/user/push/platforms/android/src/de/appplant/cordova/plugin/notification/Manager.java:25: error: cannot find symbol
import android.app.NotificationChannel;
                  ^
  symbol:   class NotificationChannel
  location: package android.app
/home/user/push/platforms/android/src/de/appplant/cordova/plugin/notification/Manager.java:43: error: cannot find symbol
import static android.os.Build.VERSION_CODES.O;
^
  symbol:   static O
  location: class
/home/user/push/platforms/android/src/de/appplant/cordova/plugin/notification/Manager.java:112: error: cannot find symbol
        if (SDK_INT < O)
                      ^
  symbol:   variable O
  location: class Manager
/home/user/push/platforms/android/src/de/appplant/cordova/plugin/notification/Manager.java:115: error: cannot find symbol
        NotificationChannel channel = mgr.getNotificationChannel(CHANNEL_ID);
        ^
  symbol:   class NotificationChannel
  location: class Manager
/home/user/push/platforms/android/src/de/appplant/cordova/plugin/notification/Manager.java:115: error: cannot find symbol
        NotificationChannel channel = mgr.getNotificationChannel(CHANNEL_ID);
                                         ^
  symbol:   method getNotificationChannel(String)
  location: variable mgr of type NotificationManager
/home/user/push/platforms/android/src/de/appplant/cordova/plugin/notification/Manager.java:120: error: cannot find symbol
        channel = new NotificationChannel(
                      ^
  symbol:   class NotificationChannel
  location: class Manager
Note: Some input files use or override a deprecated API.
Note: Recompile with -Xlint:deprecation for details.
6 errors

FAILURE: Build failed with an exception.