My shop GUI only works in studio but not in an actual sever, why not?

local player = game.Players.LocalPlayer
local currency = player:WaitForChild('leaderstats').Coins
local amount = 200
local tool = game.ReplicatedStorage:WaitForChild('LinkedSword')
local indextext = script.Parent.Text
script.Parent.MouseButton1Click:connect(function()
	if currency.Value >= amount and not player.Backpack:FindFirstChild('LinkedSword') or player.Character:FindFirstChild('LinkedSword') then
		currency.Value = currency.Value - amount		
		local newtool = tool:Clone()
		newtool.Parent = player.Backpack
		script.Parent.TextColor3 = Color3.fromRGB(11, 199, 4)
		script.Parent.Text = 'Purchase succesful!'
		wait(2)
		script.Parent.TextColor3 = Color3.fromRGB(27, 42, 53)
		script.Parent.Text = indextext
	else
		script.Parent.TextColor3 = Color3.fromRGB(255, 0, 0)
		script.Parent.Text = 'Purchase failed, you either already have this item or do not have enough coins'
		wait(2)
		script.Parent.TextColor3 = Color3.fromRGB(27, 42, 53)
		script.Parent.Text = indextext
	end
end)

script.Parent.MouseEnter:connect(function()
	script.Parent.Parent.Parent.ProductImage.Image = 'rbxassetid://'..script.ImageValue.Value
	script.Parent.Parent.Parent.Description.Text = script.DescValue.Value
	script.Parent.Parent.Parent.ProductTitle.Text = script.TitleValue.Value
	script.Parent.Parent.Parent.SwordCost.Text = script.CostValue.Value
	script.Parent.Parent.Parent.SwordDamage.Text = script.DamageValue.Value
end)

script.Parent.MouseLeave:connect(function()
	script.Parent.Parent.Parent.ProductImage.Image = 'rbxassetid://'
	script.Parent.Parent.Parent.Description.Text = ''
	script.Parent.Parent.Parent.ProductTitle.Text = ''
	script.Parent.Parent.Parent.SwordCost.Text = ''
	script.Parent.Parent.Parent.SwordDamage.Text = ''
end)

You have FE enabled. The client cannot change anything in the real server. Either disable FE(Not recommended) or use RemoteEvents to make the server do it(recommended).

Try using WaitForChild(), it works in solo play but in server play, you need to wait for everything to lad first. For example, let's say you want your GUI's to load, simply do this:

game:WaitForChild("StarterGui")

--the rest of your stuff.

Hope this helped.