Why is this CoreGui script that tweaks the Chat not working?

The script is supposed to display a message in the chat system when a brick is touched. The script works absolutely fine in Solo mode, but in Server and Online mode, it doesn't work.

I received this output though: "SetCore: ChatMakeSystemMessage has not been registered by the CoreScripts"

Can someone please help me? Here's the script:

bin = script.Parent

function onTouched(part)
    game:GetService("StarterGui"):SetCore("ChatMakeSystemMessage",{
    Text = "Domination is the chosen game mode."; -- Required. Has to be a string!
    StrokeColor = Color3.new(0,0,0);
    StrokeTransparency = 0.75;
    Color = Color3.new(255,255,255); -- Cyan is (0,255/255,255/255) -- Optional defaults to white: Color3.new(255/255, 255/255, 243/255)
    Font = Enum.Font.ArialBold; -- Optional, defaults to Enum.Font.SourceSansBold
    FontSize = Enum.FontSize.Size18; -- Optional, defaults to Enum.FontSize.Size18
    })
end

connection = bin.Touched:connect(onTouched)