Dev product not working? [HELP PLEASE!]

Hi guys! I have been trying to fix this for 2/3 weeks now and I still cannot get it work! It is really getting annoying now :/ ANY help would be appreciated! Thanks :)

I have this dev product - It lets me purchase it and it takes my money but doesn't display the gui or change the value :( Any ideas? Thanks!

Script in button in the Workspace:

local MarketplaceService = game:GetService("MarketplaceService")
local productId = 19750967
MarketplaceService.ProcessReceipt = function(receiptInfo) 

for i, player in ipairs(game.Players:GetChildren()) do
	if player.userId == receiptInfo.PlayerId then
		
		if receiptInfo.ProductId == productId then
			
		player.PlayerGui.ChoosingMap.Frame.Visible = true
		game.Workspace.ChooseMap.Value = true
		
		end
	end
end	

return Enum.ProductPurchaseDecision.PurchaseGranted		

end

localscript in the starterpack:

local buyButton = game.Workspace.Choosemapbutton.SurfaceGui.TextButton
local productId = 19750967

buyButton.MouseButton1Click:connect(function()
game:GetService("MarketplaceService"):PromptProductPurchase(game.Players.LocalPlayer, productId)
end)

Try using the event PromptPurchasedFinished(player,assetId,isPurchased). isPurchased is a bool that is true if the player accepts the purchase.

E.G:

local buyButton = game.Workspace.Choosemapbutton.SurfaceGui.TextButton
local productId = 19750967

buyButton.MouseButton1Click:connect(function()
	local market = game:GetService("MarketplaceService")
	market:PromptPurchaseFinished:connect(function(game.Players.LocalPlayer, 	productId,isPurchased)
		if isPurchased then
			-- code
		end
end)

This should be the only script you need.