Can you update this domain site https://retwtr.com/ with the correct site backend and FTP login credentials at https://stackideas.com/dashboard/site so we can access your site and investigate this issue?

Also, how do you replicate this issue on your site? Because it seems like the registration work fine for me. (screenshot: https://monosnap.com/file/Sbo31duTUvkQtE00WyJks4eBBUiIeX )