So here is the code accessing the local script~
player.PlayerGui.ChangeMoneyGui.RemoteClient:FireClient()
and here is the code receiving the event.
local player = game.Players.LocalPlayer script.RemoteClient.OnClientEvent:connect(function() player.PlayerGui.Money.Money.Text = "Money: " .. player.leaderstats.Money.Value end)
Anytime I try to call the event I get the error "Argument 1 missing or nil". All the code seems fine so what's the issue. The first script is a script inside workspace. The second is a local script within the players GUI.
It's because your script that is located on the server is confused on which client to send its request to.
Try this:
player.PlayerGui.ChangeMoneyGui.RemoteClient:FireClient(playerName)