This issue is caused by square_in_app_payments package using deprecated Android v1 embedding. Starting Flutter 3.29.0, Flutter does not support v1 embedding. So the package should be upgraded to support Flutter 3.29.0.

Here's an issue opened in square/in-app-payments-flutter-plugin repo: https://github.com/square/in-app-payments-flutter-plugin/issues/259

You can try

1. Wait for the new version of package. (You can watch the issue on Github.)
2. Downgrade Flutter to 3.27.4
3. Fork and Fix It Yourself: Refer to Flutter’s official migration guide for deprecated plugin APIs here: https://docs.flutter.dev/release/breaking-changes/plugin-api-migration (Copied from the answer below)

This answer might be helpful: https://stackoverflow.com/a/79465363/10202769