Unable to add folders to libraries in PMS

I have a question:

Is PMS running on the synology or on Windows?

You show pathnames which are Windows syntax: I:/TV/The Shield
That’s Windows. Linux pathnames are what Synology uses. (No drive letters)

I see where PlexMediaServer was installed.

A few rules:

  1. On Synology, there are no drive letters . All pathnames begin with /volumeX/shared_folder_name (X = 1, 2, 3, etc)

  2. Have you looked at the setup guide for new users ?