Why isn't this this script working?

So I'm confused because i did everything the roblox wiki told me to do in this script but it still doesn't work. Can anyone tell me why? Thanks if you did!

Script:

local plr = script.Parent.Parent.Parent.Parent
local MarketplaceService = game:GetService("MarketplaceService")
local cashid = 22957008
local PurchaseHistory = game:GetService("DataStoreService"):GetDataStore("PurchaseHistory")


function addcash()
    if plr then
        local leaderstats = plr:FindFirstChild("leaderstats")
        if leaderstats then
            local cash = leaderstats:FindFirstChild("Cash")
            if cash then
                cash.Value = cash.Value + 10000
            end
        end
    end
end

script.Parent.MouseButton1Click:connect(function()
    MarketplaceService.ProcessReceipt = function(receiptInfo) 
        local playerProductKey = receiptInfo.PlayerId .. ":" .. receiptInfo.PurchaseId
        if PurchaseHistory:GetAsync(playerProductKey) then
            return Enum.ProductPurchaseDecision.PurchaseGranted --We already granted it.
        end
        -- find the player based on the PlayerId in receiptInfo
        for i, player in ipairs(game.Players:GetPlayers()) do
            if player.userId == receiptInfo.PlayerId then
                -- check which product was purchased (required, otherwise you'll award the wrong items if you're using more than one developer product)
                if receiptInfo.ProductId == cashid then
                    addcash()
                end
            end 
        end
        -- record the transaction in a Data Store
        PurchaseHistory:SetAsync(playerProductKey, true)    
        -- tell ROBLOX that we have successfully handled the transaction (required)
        return Enum.ProductPurchaseDecision.PurchaseGranted     
    end
end)