how to require a valid email to download items like mp3, pdf, etc

I am using WordPress Download Manager, however, I want to be able to put a link up to a download, and require a valid email address to allow access to the file (mp3, image, pdf,etc).

Currently I am trying to use the Member-Only feature of the plugin, but cannot get it to work. They have the example ofhttps://yourdomain.com/wp-login.php?redirect_to={referrer} in the configuration panel, but it is not doing it for me. how would I use it properly so that the person is taken to register and then back to the page they were on?

I am currently using a plugin called Register Plus for email verification.

I really just want to offer a link that requires a valid email to download the file. any help out there?