I need more info about GSSteamBuyGoodsRequest Node...
1.How can I get the OrderID?
2.Should I make the Virtual Goods in Steam Account?
The order ID is given to you when you use Steam SDK to make a purchase resulting in a receipt. It is a unique 64-bit ID for order.
Yes you need to have a steam store item, and a counter part in your GameSpark game as a virtual item.