Plex shows a green checkmark / remote access status indicator while testing the connection. So if it switches from green to red after a few seconds (up to 1-2 minutes), that simply means your remote access isn’t working to begin with.
Did you already have a look at the related troubleshooting support article?
https://support.plex.tv/articles/200931138-troubleshooting-remote-access/
There’s also a guide with some more details on how to troubleshoot remote access issues.
Have you already verified if there’s an IP reservation for your server and a port forward for Plex (public port can be random, private side must point to the server’s local IP and tcp port 32400).
