For future reference, in order to add a GIN first it has to be done before anyone bids on your auction, because the auction is locked in after someone bids. When you are listing your auction, you go to advance options and the GIN option will be there. If you are adding a GIN to an auction you have already listed, you have to go to advanced options after clicking edit. Also, GIN options don't go below 2,000 credits so the GIN you chose would have been too low. And you should make your GINs higher not only because Listia takes 10% of your GIN credits, but because a GIN should be worth the items and shipping. Four books in a collection are worth at least 15,000 credits if you are underestimating for a GIN price or trying to be nice. I hoped this helped and I hope you have a wonderful experience on Listia. Good luck with this and future auctions! ;)