Plutonium

from Pluto's main menu > server browser > select a server and hit connect to server

Is this a menu you coded yourself or is this a menu you downloaded? Most if not all menus that were made for players that inject it are coded to give the menu to players that are host, using the isHost() function. That won't work if you're using it on your server as that function will return false for all players. If this is the case and you know a bit of GSC, you can fix this by changing the check in onPlayerSpawned() from if(player isHost()) to if(player getXUID() == "yourXUIDhere")

This is all assuming your server is parsing the file.