When I do the username and mod name and reason, it just sends it back to me, Only me I tested it with two players I done it to the other player and it send back to me again.
My code:
game.Players(script.Parent.Parent.Username).PlayerGui.WarnGui.Enabled = true
Is this script client-sided or server-sided?
Any code run on the client is only going to be seen by that client, unless replicated to the server in some way.
It probably isn’t since OP wrote script.Parent.Parent.Username in their script.
I would personally use remote events though you can just create a script in ServerScriptService, and add the code below:
local Players = game:GetService("Players") -- The players service
for _, player in Players:GetPlayers() do -- Getting all the players inside a table and looping through them
player.PlayerGui.WarnGui.Enabled = true -- Setting their WarnGui.Enabled property to true thus making it visible
end