I've been trying for about an hour now and I'm not sure what is with this script that I'm messing up on. So this is going to subtract 1 every second from the NumberValue I placed in workspace which will affect the text in a text label. This is a serverScript placed in StarterPlayerScripts, the text label is in starter gui under a screengui and frame. Number value is in workspace.
valueThing = game.Workspace.Value.Value
plr = script.Parent.Parent.PlayerGui.TimeScreen.Frame.TextLabel.Text
while true do
plr = valueThing
valueThing = 500
wait(1)
valueThing = valueThing - 1
end

3 comments
It's OnClientEvent, not OnClientInvoked. Also might wanna tell him that he should fix his .Value property, as you changed it in the code (which is correct), but you don't mention anything about it.
"Filtering Enabled is likely on" =>Just for sake of correctness, filtering is now always enabled regardless of FilteringEnabled’s Value.
@RubanKan Thanks for catching that