Hi there @KSA_Developer,
I think the problem is just that you have the wrong name for the function call.
It’s not:
plugin:SelectRibbon(Enum.RibbonTool.None, UDim2.new(0,0,0,0))
rather its:
plugin:SelectRibbonTool(Enum.RibbonTool.None, UDim2.new(0,0,0,0))
SelectRibbonTool, not SelectRibbon.
I was able to recreate both the error and a fix in my own plugin.
Please try and report back if this helps you?