I am trying to make a simple shop gui but cant use the dev products. Ideas?

I am trying to make a ui that you can buy coins but for some reason when I call the marketplaceservice prompt purchase event I get the error "unable to cast value to object". Any ideas?

for _,v in pairs(PlayerGui:WaitForChild("BuyCoinsUI").Main.PackageFrame:GetChildren()) do
	if v:IsA("ImageLabel") then
		v.PurchaseCoins.MouseButton1Click:Connect(function()
			PlayClickAudio()
			if v.Name == "BasicCuberPackage" then
				print("basic bought")
				MarketplaceService:PromptProductPurchase(player.UserId, 975968181)
			elseif v.Name == "AdvancedCuberPackage" then
				print("advanced bought")
				MarketplaceService:PromptProductPurchase(player.UserId, 976009690)
			elseif v.Name == "LegendaryCuberPackage" then
				print("legendary bought")
				MarketplaceService:PromptProductPurchase(player.UserId, 976010896)
			end
		end)
	end
end

I'm going to make the assumption that you have all your variables well-defined and that your player variable is not set as the character but as the player itself.

According to the Roblox Documentation, you need to refer to the player itself - not their UserID. You can find more about that here.

Your script should look like what I have below.

for _,v in pairs(PlayerGui:WaitForChild("BuyCoinsUI").Main.PackageFrame:GetChildren()) do
    if v:IsA("ImageLabel") then
        v.PurchaseCoins.MouseButton1Click:Connect(function()
            PlayClickAudio()
            if v.Name == "BasicCuberPackage" then
                print("basic bought")
                MarketplaceService:PromptProductPurchase(player, 975968181)
            elseif v.Name == "AdvancedCuberPackage" then
                print("advanced bought")
                MarketplaceService:PromptProductPurchase(player, 976009690)
            elseif v.Name == "LegendaryCuberPackage" then
                print("legendary bought")
                MarketplaceService:PromptProductPurchase(player, 976010896)
            end
        end)
    end
end

If this helps, consider accepting this answer. If not, comment below and I'll help you out further.