Can't complete registration - no relevant button shown

We're using Protected Content (with Gravity Forms for the registration form) to create a simple membership site - one member level, only a few protected pages.

The membership level is free = no payment gateway is configured.

Right now users can't complete registration at all because the 3rd page in the flow gives them this message: "Please check the details of the membership below and click on the relevant button to complete the signup." Screenshot here: http://pbrd.co/1rS2ZGA

The problem is that there is no button to complete the signup. I've seen a lot of threads about this for the Membership plugin but none with solutions.

Also it seems that at this point the users are already added to the site, and can access the protected pages, but there's no way that they would know that based on this misleading message.

We've tried the default theme and turning off all other plugins. The problem is the same - no final button.

We need a solution to this asap since this site needs to go live this week, so thank you in advance for your assistance!