nothing happens with sign-up button!

I've installed membership plugin and setup some access levels and subscription plans. I've also configured and activated a gateway.

My problem lies in the registration page (the page from where one can get a subscription -- parabing.com/register/). When I click the sing-up button for any subscription, the page reloads (with what seems to be the appropriate GET parameters), but nothing else happens! I was expecting a form for actually buying the selected subscription, but nothing appears...