Well I got gift giftcards.com to work with an Amex ironically 2 weeks ago (naturally with no success tracking in AA) and because I’m a masochist I tried again on 4 different cards and each time I get the following by email from them:

We had to cancel your order #XXXX because it didn’t pass our screening process. Online security is important—like really important—so we take every measure we can to protect the people shopping with us.We suggest you check out your billing and shipping info—there might be an oopsie in there that needs fixing!