Isn't working

So, I installed this module using composer and installed on my drupal website,
added this code in settings.php

set_error_handler(['Drupal\error_page\ErrorPageErrorHandler', 'handleError']);
set_exception_handler([
'Drupal\error_page\ErrorPageErrorHandler',
'handleException',
]);

// Log the UUID in the Drupal logs.
$settings['error_page']['uuid'] = TRUE;
// Your templates are located in path/to/templates, one level above the webroot.
$settings['error_page']['template_dir'] = DRUPAL_ROOT . '/web/modules/contrib/error_page/markup';

// To test out error page test
$settings['extension_discovery_scan_tests'] = TRUE;

but whenever i direct to an error page, it doesn't show what it suppose to show.

Is there any step i missed?