@Don - It has an unlimited amount of uses if you log out as a guest. I don't know if this also happens when you are logged in since I wasn't logged in for my original order.
@TheDiamondKing23 - Welcome to the discourse! As Don said in the post directly above yours, the D&D code should work for all not card-related items in your cart. If you didn't have only playing cards and this still didn't work, make sure you typed it perfectly correctly!