Why are end-users are receiving an "oops - The page you were looking for doesn't exist" error when submitting tickets via the Help Center?
This error is displayed when a 404 Not Found console error occurs while loading a page. When an end-user receives this message upon submitting a ticket from your Help Center, it is likely caused by a trigger that is adjusting the brand of that ticket.
To confirm this you will want to locate the ticket in your Support account and the ticket audit trail. If at any point the brand of the ticket is adjusted, then the error is expected behavior. This is due to the fact that when a ticket's brand is adjusted, that ticket will then be located on a different Help Center. In order view that ticket the end-user would need to sign into the other brand to view that specific ticket.