ProSites – Page not found error after user submits payment info

My users are getting a page not found error upon completing the registration process. They enter their site info, then payment info, then when they submit, a 404 loads.

I have gone back over the Pro Site settings to double check I haven’t missed something and I can’t find anything. This was working previously though I am not 100% certain when exactly it broke.

I have granted support access, should you need it.