/msg

Sends a private message to one or more players. Also available as /tell and /w.

Syntax

/msg <targets> <message>

Name	Type	Required	Description
targets	entity	Required	The player(s) to send the private message to.
message	message	Required	The message text to send.

/msg Steve Hey, come to my base!

Sends a private message to Steve.

/msg @a Server maintenance in 5 minutes

Sends a private message to all players.

Using /msg for public announcements, other players will not see the message. Use /say for public messages.
Forgetting that @a sends individual private messages to each player, not a group message.

Available to all players (permission level 0). Aliases: /tell, /w. The message is only visible to the sender and the targeted player(s).

Try these commands on Astroworld or host your own server.