How do I make this work? ProcessReceipt not working not giving errors

local marketplaceService = game:GetService("MarketplaceService")

marketplaceService.ProcessReceipt = function(purchaseInfo)
    local plr = game:GetService("Players"):GetPlayerByUserId(purchaseInfo.PlayerId)
    if purchaseInfo.ProductID == 122550429 then
        game.Workspace.FrenzySpawns.FrenzyValue.Value = 5
        game.StarterGui.ScreenGui.FrenzyNotifier.Visible = true
        game.StarterGui.ScreenGui.FrenzyNotifier.Announcement.Text = "test"

    end
    return Enum.ProductPurchaseDecision.PurchaseGranted
end