Attempt to index local 'player' a nil value?

Alright so I made a gun buying GUI for a street dealer and it won't buy the gun or take the money away due to the error aforesaid in the title.

    local player = game:GetService("Players").LocalPlayer
    local money = player:WaitForChild("Money")

function BuyAK()
 	if money.Value >= 125 then
		money.Value = money.Value - 125
			local AK47 = game.ServerStorage.AK47:clone()
			AK47.Parent = script.Parent.Parent.Parent.Parent.Parent.Backpack
			script.Parent.Text = "Gun Purchased"
		wait(5)
			script.Parent.Text = "Buy AK-47"
	   else
		    script.Parent.Text = "Purchase Failed"
		wait(5)
		    script.Parent.Text = "Buy AK-47"
	end
  end


script.Parent.MouseButton1Down:connect(BuyAK())