A Momento API Token is required. You can generate one using the Momento Console.
Add the module with composer require momentohq/drupal-cache:dev-main and enable in Drupal.
Add the following to your settings.php file, replacing <YOUR_MOMENTO_TOKEN> with the token you generated in the console.
$settings['cache']['default'] = 'cache.backend.momento_cache';
$settings['momento_cache']['auth_token'] = <YOUR_MOMENTO_TOKEN>;