Additional Information
Plex Forum Tips Tricks & How Tos → The Basics of Remote Access Troubleshooting
Plex Documentation → Remote Access and Server Sharing
→ Remote Access
→ Troubleshooting Remote Access
CanYouSeeMe.org: To check that remote access port is open
From a system on the same network as your Plex server, go to the website.
The Public Address should match what is shown on the Plex Remote Access settings page.
Enter your remote access port number and choose Check Port. It will report back whether or not it can reach your server.