Is it possible to re-direct the customer to another page upon completing payment as opposed to the standard "Registration Completed" page? I have an additional registration form I need the customer to complete and would like to have them go to that page instead.
It is not possible, unfortunately. If you want that, you can submit a support ticket sending us super admin account of your site and tell us url of the page you want users to be redirected to
I am going to edit the code to get it works for you