Just installed pro sites for the first time and a 404 error

I have just installed pro sites and once enabled my domain.com/wp-signup.php is changed to http://travel.optinenterprise.com/enterprise-sites/?action=new_blog which gives back a 404 error.

From within the settings section, I can see that I can edit the checkout page. The page exists and the body is empty.

Not sure why this is throwing a 404.