Settings page has nothing on it

Is this plugin still working? I added it and the settings page has nothing except the option to choose if signup is only for people invited.

I chose that, open the website not logged-in and can see the whole website, so I am not sure how it is suppose to work..

Hope someone can help me with that. Really want to have my website as an invite-only website.

Thanks!

https://www.ads-software.com/plugins/wordpress-mu-secure-invites/