It a known issue for several months but fab staff havent look into it yet.
Try to post all detail here: Fab Purchasing issues, "Looks like something went wrong. For your protection, this transaction has been declined. Please try another card or other payment methods."
and contact them on https://support.fab.com/s/?ProductOrigin=FabSupport and also include the link above in the message form so that the staff know it a common problem with the payment system being broken for lot of people.