Getting the below error on adding the flutter downloader

flutter doctor output:
```
Doctor summary (to see all details, run flutter doctor -v):
[✓] Flutter (Channel master, 1.24.0-8.0.pre.356, on Mac OS X 10.15.7 19H2
darwin-x64, locale en-GB)
[!] Android toolchain - develop for Android devices (Android SDK version 30.0.2)
! Some Android licenses not accepted. To resolve this, run: flutter doctor
--android-licenses
[✓] Xcode - develop for iOS and macOS (Xcode 12.3)
[✓] Android Studio (version 4.1)
[✓] IntelliJ IDEA Community Edition (version 2020.3.1)
[✓] Connected device (1 available)

! Doctor found issues in 1 category.

```
**/Users/thinkpalm/Office/flutter/.pub-cache/hosted/pub.dartlang.org/flutter_downloader-1.5.2/android/src/main/java/vn/hunghd/flutterdownloader/DownloadWorker.java:456: error: cannot find symbol
notificationManager.createNotificationChannel(channel);
symbol: method createNotificationChannel(NotificationChannel)
location: variable notificationManager of type NotificationManagerCompat**