This is an AA specific question - even though its related to an AmEx Benefit... so please mods - read through the question before booting me over to the AmEx forum.... LOL - thank you !!

Ive just realized that I havent used my $200 AmEx Platinum airline fee credit so Im thinking of using it for purchase of miles through the mileage multiplier option (as I understand this benefit is not valid for outright purchase of AA miles).

So then, I remember that the mileage multiplier option comes up somewhere at the end of the purchase/payment process when you do this on the AA website. My question is, are you able to use 1 credit card to purchase the ticket, but another different card to pay for the mileage multiplier option..? This is because I would want to your my Citi AA card for the purchase of the ticket but my AmEx card for the multiplier option.

If this isnt possible, is there a way for me to purchase only the mileage multiplier after my ticket has been issued....? I vaguely remember this option being offered at the airport check-in kiosks but nowadays I rarely use these.... so is there a way to buy these multipliers on the phone, or using the app....?

Thanks !!