https://www.aa.com/i18n/utility/FAQs...ingOptions.jsp
Please note that for AA.com bookings in the U.K. paid with a credit card or PayPal, a processing fee of £4.50 per ticket will be charged. The processing fee does not apply to U.K. bookings paid with a debit card. This fee is refundable only for refundable tickets.
For about a week or so (at least based on when I first noticed it), the following has been disclosed when booking on AA.com...
If you choose to pay using a credit card or U.K.-billed PayPal account, a processing fee of £4.50 per ticket may apply