Symfony\Component\Debug\Exception\FatalThrowableError : Class 'Seeder' not found

The error message "Symfony\Component\Debug\Exception\FatalThrowableError : Class 'Seeder' not found" indicates that the class 'Seeder' cannot be found in your Symfony application. This error typically occurs when the autoloader is unable to locate the class file.

To resolve this issue, you can follow these steps:

1. Make sure the 'Seeder' class exists in your Symfony project. Check the file path and ensure that the class is defined correctly.

2. Check if the 'Seeder' class is properly namespaced. In Symfony, class names are often namespaced to avoid naming conflicts. Ensure that the namespace declaration in the 'Seeder' class file matches the namespace you are using in your code.

3. Confirm that the autoloading is set up correctly. Symfony relies on an autoloader to automatically load classes when they are needed. Check your autoloading configuration, typically located in the 'composer.json' file, and make sure it includes the appropriate paths for your 'Seeder' class.

4. Run the Composer command composer dump-autoload to regenerate the autoloader files. This command will update the autoloader to include any new classes or changes you have made.

By following these steps, you should be able to resolve the "Class 'Seeder' not found" error in your Symfony project.