I just installed Plex Media Sever today and had to connect to (hostname):32400/web from a system on the same subnet in order for it to let me register it.
The server is using the latest non-beta build for Linux but I was able to reproduce this behavior on my Windows PMS server as well.
I was able to access the server directly via web browser, and logging in did give me the plex shell but the option to claim/register it was not presented until I went to the server from a system on the same IP subnet.
Server’s IP is 192.168.4.21
Desktop IP is 192.168.3.40
I verified that the following ports were allowed through the firewall router
1900,3005,5353,8324,32400,32410,32412,32413,31414,32469
Is this a safety built into the platform by design?