Wheres the promotional code on my gamestop card?

I went to gamestop and traded in a BUNCH of games and had him put all the money on a card. It was about 300 bucks in total. I was in a hurry so i just took the card and went home. Im on the gamestop site and i want to order some games. Its asking me to enter my promotional code, but im not finding where this '' code '' is on the card the guy gave me.