how do users create a site using Pro Sites?

I'm using User Meta Pro* for my user registration.

I have my network settings set to "Logged in users may register new sites."

However, when I visit the checkout page, I get this message:

"Sorry, but it appears you are not an administrator for any sites."

So there doesn't seem to be any way for them to sign up. Ideas?

Thanks!

*although its extremely buggy and they have terrible support... here's hoping you create an alternative to their plugin someday!