Why is this Dev Product Not Selling?

The following script below is the handler for my developer product. Everything seems to work, but it says in the output that User id is not a valid member of folder. Does anyone have any ideas?

local MarketPlaceService = game:GetService('MarketplaceService')
local devProductID = 137200600 --1000 cash

MarketPlaceService.ProcessReceipt = function(receiptInfo)
	for i, player in ipairs(game.Players:GetChildren())do
		if player.userId == receiptInfo.PlayerId then
			if receiptInfo.ProductId == devProductID then 
				player.leaderstats.Cash.Value = player.leaderstats.Cash.Value + 1000
			end
		end
	end
	return Enum.ProductPurchaseDecision.PurchaseGranted
end