So you did not use the Amex card that the offer was attached to? The one that, when you see the offer in your Amex account you click "add to card"? Of course it's not going to work! I had a situation where I was an authorized user on the amex-offer card (my husband was the primary), and even that didn't work - luckily it was at a store (Staples) so I brought the stuff back and had them recharge it on my husband's card (same account, different number). Now I'm very careful to know which card number offers are attached to.