I was using the mod pretty well for a while, but now suddenly certain players are not allowed to join or create playlists, making it impossible to access any features on PC. The music player works fine. I'm on a 1.16.5 server.

Hello, if you are on a server, what worked for me was to delete the mod, that is, the .jar and the iammusicoplayer folder that is in the wolrd folder, open the server and turn it off and place the mod again and it worked (1.16.5)

Delete folder "iammusicplayer" in your world folder