flutter_launcher_icons

pubspec.yaml

dependencies:

  flutter:

    sdk: flutter

  flutter_launcher_icons: ^0.9.3

flutter_icons:

 image_path: "assets/icon.png"

 android: true

 ios: true

Perfect. Now you can run flutter pub get to get and update all mentioned dependencies in pubspec.yaml. The next step is to run the command.

flutter pub run flutter_launcher_icons:main 

======================

if have error:

Adding
flutter.minSdkVersion=21
to android/local.properties solved the issue for me.

See

https://github.com/fluttercommunity/flutter_launcher_icons/blob/master/lib/android.dart

which calls
getMinSdkFromFile(androidGradleFile)