How can I grant my Developer Product correctly?

Hello! I'm having trouble getting my Developer Product to grant the product, in this case 100000 Points. When I test it in Studio, I can click on my Surface Gui to bring my shop screen up, I click on the product, "Purchase 100000 Points", the screen pops up to confirm the purchase...but then the Points aren't added. I receive this error:

23:22:41.888 - userId is not a valid member of BoolValue

I'm not sure why my userId is not valid, I've seen the script laid out this way elsewhere.

Also, when I do a local server test, my Screen Gui won't appear at all when I click it, same for when I upload my game to Roblox itself and try. Any thoughts?

Here's my code below for the developer product:

local MarketplaceService = game:GetService('MarketplaceService')
local devproductid = 48677962 --  DevId to Grant 100000 Points

MarketplaceService.ProcessReceipt = function(receiptInfo) 
	for i, player in ipairs(game.Players:GetChildren()) do
		if player.userId == receiptInfo.PlayerId then
			if receiptInfo.ProductId == devproductid then
				
			-- give them the Points
player.leaderstats.Points.Value = player.leaderstats.Points.Value + 100000
			end
		end
	end
	return Enum.ProductPurchaseDecision.PurchaseGranted
end

And then I have this code inside the Text Button, inside the Frame, inside my Screen Gui inside Starter Gui:

local button = script.Parent
local devproductid = 48677962 -- 100000 Points

button.MouseButton1Click:connect(function()
	game:GetService('MarketplaceService'):PromptProductPurchase(game.Players.LocalPlayer, devproductid)
end)

Thank you!