So some online retailers allow you to checkout using the American Express website instead of entering your card details. More secure, no entering card info at the merchant level. So everytime I try and register the card I get an error code saying it wont work at American Express. I called USAA and they seemed clueless to my problem and arent even aware of it. Mastercards service worked when USAA used it. My VISA with USAA work with their own check out service.