saml_login -> 404 Not Found

Hello,
when accessing to http://example.com/saml_login it shows a 404 error page. I have configured the SimpleSaml path in settings.php:
$settings['simplesamlphp_dir'] = '/var/www/vhosts/example.com/sp.example.com';

SimpleSaml SP is installed on sp.example.com whilst Drupal is installed on example.com. The SP works correctly, and the authentication source is correctly configured.

The error I get in my logs is:
File does not exist: /var/www/vhosts/example.com/httpdocs/saml_login, referer: http://example.com/user/login

(Drupal is located at /var/www/vhosts/example.com/httpdocs)

Thanks!