Hi, I am not very familiar with reverse proxying in general so anything that points me in the right direction is welcomed.
I am aware that vercel recommends against doing this but this project is already setup to work this way and I am just looking to migrate it to a more cost effective solution. (WPEngine hosting is very expensive)

In short, currently this project is a "headless" WordPress application. However, some parts of the website are still utilizing a WordPress front end. So for the time being the server that is hosting the WordPress website is using reverse proxy to make the Next App appear to be part of the same website.

Currently this setup works
xxx.com (WP Website) is using reverse proxy to make (xxx.wpengine.com) seem like its part of it

The new setup
xxx.com (WP Website) is using the same reverse proxy configuration to point to xxx.vercel.com but its instead displaying an error.

The error is a vercel error so I know that the WP host is pointing to the right place, but I am not sure why the "deployment" is not found.
I did already triple check that xxx.vercel.com does exist, it is the primary domain, and it is public.

Thanks in advance!