"make a script for leaderstats called Money and make a gui on the side of the screen where you can buy 100 Money 1539630478"

-- script for leaderstats 
local Players = game:GetService("Players")

local function onPlayerAdded(player)
    local leaderstats = Instance.new("Folder")
    leaderstats.Name = "leaderstats"
    leaderstats.Parent = player

local Money = Instance.new("IntValue")
    Money.Name = "Money"
    Money.Value = 0
    Money.Parent = leaderstats
end

Players.PlayerAdded:Connect(onPlayerAdded)

-- local script for GUI 
local button = script.Parent
local MarketplaceService = game:GetService("MarketplaceService")
local productId = 1539630478

local function onButton1Down()
    local player = game.Players.LocalPlayer
    MarketplaceService:PromptProductPurchase(player, productId)
end

button.MouseButton1Click:Connect(onButton1Down)

-- server script for handling product purchase 
local MarketplaceService = game:GetService("MarketplaceService")

local function processReceipt(receiptInfo)
    local player = game.Players:GetPlayerByUserId(receiptInfo.PlayerId)
    if player then
        local leaderstats = player:FindFirstChild("leaderstats")
        if leaderstats then
            local Money = leaderstats:FindFirstChild("Money")
            if Money then
                Money.Value = Money.Value + 100
            end
        end
    end
    return Enum.ProductPurchaseDecision.PurchaseGranted
end

MarketplaceService.ProcessReceipt = processReceipt