What does this PromptProductPurchase error mean?

PurchasePromptScript: getProductInfo failed because MarketplaceService:getProductInfo() failed because rawProductInfo was empty Make sure a valid ID was specified <

LocalScript:

local MPS = game:GetService("MarketplaceService")
local RPS = game:GetService("ReplicatedStorage")

script.Parent.MouseButton1Click:connect(function()
    MPS:PromptProductPurchase(game.Players.LocalPlayer, 643910613)
end)

RPS.Events.BuyPrompt.OnClientEvent:connect(function(player, product)
    if product == "Upgrade" then
        script.Parent.Text = "You Own This Item"
    end
end)

Main Script:

local MPS = game:GetService("MarketplaceService")
local RPS = game:GetService("ReplicatedStorage")
local product = ""

MPS.ProcessReceipt = function(purchaseInfo)
    local player = game:GetService("Players"):GetPlayerByUserId(purchaseInfo.PlayerId)
    if purchaseInfo.ProductId == 643910613 then
        product = "Upgrade"
        RPS.Events.BuyPrompt:FireClient(product)
    elseif purchaseInfo.ProductId == 653173240 then
        product = "Elite"
        RPS.Events.BuyPrompt:FireClient(product)
    elseif purchaseInfo.ProductId == 659939994 then
        product = "Palace"
        RPS.Events.BuyPrompt:FireClient(product)
    end
    return Enum.ProductPurchaseDecision.PurchaseGranted
end