I want to use the Flutter package webview_cookie_manager in my Flutter project. It has been working normally in the past, but now I get an error message when I try to run it.

For Testing purposes I created a completely new project:

flutter create test
cd test
flutter run

which works as usual. However, when I add the package:

flutter pub add webview_cookie_manager
flutter run

I get the following error message:

FAILURE: Build failed with an exception.

* What went wrong:
A problem occurred configuring project ':webview_cookie_manager'.
> Could not create an instance of type com.android.build.api.variant.impl.LibraryVariantBuilderImpl.
   > Namespace not specified. Specify a namespace in the module's build file. See  for information about setting the namespace.

     If you've specified the package attribute in the source AndroidManifest.xml, you can use the AGP Upgrade Assistant to migrate to the namespace value in the build file. Refer to  for general information about using the AGP Upgrade Assistant.

* Try:
> Run with --stacktrace option to get the stack trace.
> Run with --info or --debug option to get more log output.
> Run with --scan to get full insights.
> Get more help at .

BUILD FAILED in 10s
Running Gradle task 'assembleDebug'...                             11.6s

I searched for a solution and found that I could either somehow add a namespace as the error message suggests, but I couldn't get it working, or I could downgrade the Android Gradle Plugin, which I also didn't manage.