Chat:sendSystemMsg(content, targetuin) 

Where:

• content string (The message that will be sent)
• targetuin number (The Uid of the player that will see the message)

And returns:

• ErrorCode.Ok number (0 if execution was succesful and 1001 if the execution failed)

When a player joins, he will see a message.

ScriptSupportEvent:registerEvent([=[Game.AnyPlayer.EnterGame]=], function(e) 
 
    local playerid = e['eventobjid']
    local _, playernick = Player:getNickname(playerid)
 
    Chat:sendSystemMsg("Welcome, " .. playernick, playerid)
 
end)