I'm trying to book a flight using Avios on AA metal on the BA site. Flights are showing as available on BA.com, I make the booking, I get the payment authorisation screen, payment is authorised, then the "Thank you for booking your reward travel with British Airways" screen flashes up briefly, then "Sorry we have been unable to complete your transaction at this time" and a message to contact my BA office.

Is the only way to book if I call or is there something I should be doing?