You cant make server changes from the client and the server can’t manage UI input.
You need to have your local script detect when a UI button is pressed, fire a remote event to the server then the server does the calculation logic and adds +0.1
just to check, I make a function in another script that does what this does and when it is clicked it sends the remote evnet and fires the function from the other scirpt,.
-- Local script
myUIButton.MouseButton1Click:Connect(function() -- user presses button
myRemoteEvent:Fire() -- fire remote to the server
end)
---------------------------------------------------------
-- Server Script
myRemoteEvent.OnServerEvent:Connect(function(player) -- server detects remote was fired
-- do logic on the server
end)