We do have a specific Facebook sign up form tool for you to use instead of the URL. Make sure you are clicked onto your Contact Growth Tools page and you will see on the right hand side an option for Facebook Sign-Up Form. When you click on that option it will walk you through the steps of creating that form!
I am having the same problem - the sign up form is there but I can click the button. It changes to a lighter shade colour but doesn't click and register the new contact to set mailing list. Please offer your advice
Thank you for reaching out to the Community! Can you please give us some more information about what you are trying to select? Are your contacts not able to sign up due to an unresponsive button? Also, please provide a screenshot or a link to the form so we can take a look.