You should consider the indentation for assets
Flutter uses the Pubspec.yaml file, located at the root of your project, to identify assets required by an app.
Here is an example:
flutter:
assets:
- images/pizza1.png
- images/pizza0.png
More details:
flutter:
[2 whitespaces or 1 tab]assets:
[4 whitespaces or 2 tabs]- images/pizza1.png
[4 whitespaces or 2 tabs]- images/pizza0.png
Note: Only files located directly in the directory are included unless there are files with the same name inside a subdirectory . To add files located in subdirectories, create an entry per directory.