I've successfully installed the Music Playlist plug-in and Plex Playlist Manager on Windows 10. The Playlist Manager correctly matches my Windows Media Player playlists (exported as m3u files) and identifies the tracks I can save as a Plex Playlist.
However when the playlist is saved it's empty. Also it's not possible to delete it a message "Not supported yet" is displayed.
Any advice as to where I'm going wrong would be welcome.