Unable to remotely access my server

Remote access is not linked to the app activation or a Plex Pass membership.
There’s a number of different elements when it comes to remote access – so you’ll probably need to dig a bit deeper what exactly is causing this.

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…