[HowTo] Use Plex with No Internet
Plex assumes the Internet is always available.
The app that is installed on SmartTVs (LG, Samsung, etc.) is not the full version. When launched, it checks on the Internet then downloads the full version of the app.
You can use your phone as a hotspot for the check-in process. Then, without turning off the TV or launching any other apps, switch it back to your home network.
Read the guide. There are some server settings required as well. You’ll need to allow access without authorization (settings → network). Authorization requires communication with plex.tv, which is not possible if the Internet is out.
