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Load the Local Version of Plex Web App
You first need to launch the local version of Plex Web App rather than the hosted version. For instance, if you’re on the computer running the Plex Media Server, you can go to: http://localhost:32400/web or http://127.0.0.1:32400/web
See the related article for details on how to access “locally”.
The linked article says
Local Plex Web App
Your Plex Media Server comes bundled with a local version of the Plex Web App. This allows you to manage your Server and access content even if you don’t have an internet connection available.
You can open Plex Web App in a variety of ways, depending on which platform and computer you’re using.
Accessing Plex Web App Directly in the Browser
On all platforms, you can access Plex Web App on your local network. From any computer on the local network:
http://[Local Plex Media Server IP Address]:32400/web
(e.g. http://192.168.1.25:32400/web) Or locally, from the computer running the server:
http://localhost:32400/web
or
http://127.0.0.1:32400/web
