How to get remote access with a reverse proxy on port 80

I can access Plex via my domain at plex.example.com. It’s a nice friendly domain for my users to connect to. I have other web servers, not just Plex.

I have a reverse proxy using ngnix which changes plex.example.com on port 80 into localhost:32400.

I’ve changed the Custom server access URL to plex.example.com.

But I’m not sure how to get remote access.

What do I put for "Manually specify public port ". I’ve put 80, that doesn’t work. It seems to be trying to connect to my Plex server via my external IP address?

I plan to use ssl and forward port 80 to 443 in the future, just not now.

Thanks.

Is Custom server access URL even working? I read reports on another thread that it was broken.

Any status on this? Been trying to get it to work but unsure if its user error or not.