You don’t need the PlayerAdded or removing events if doing it outside, as your use case is completely unrelated to specific players - shutting down the server should be shown to all players in the servers at that time so can just do Players:GetPlayers at the time or even a remote event with FireAllClients then you don’t have to worry about the player list at all.
Regarding the error, where are you testing this? If it’s in studio then perhaps the API services access in studio is not enabled for that game.
Edit: after a very brief search, MessagingService: Service disconnected
Always use the search bar before posting.