Yes, I used my Amex Platinum card reflexively for the 5X airline bonus, but they made me use one of the secure payment systems that seem to indicate it was not going to be processed by Frontier. They seemingly have outsourced this status match program. It wasn't enough money for me to stop the transaction and try to figure out an alternative card payment. Indeed, the first time I tried to sign up, it would not let me because it could not recognize my legacy (short number) Frontier frequent flyer number. I was thrilled just to be able to complete the transaction. 😀