It showed one seat available and I'm only trying to get one seat. Even just now I tried it again it shows availability and then when I'm ready to pay for the tax on that one seat, last page says "Sorry, we have been unable to complete your transaction at this time. We're sorry, we are unable to process your request. Please contact your local British Airways office". I tried multiple credit cards.
But when I call British Airways they won't honor what appears on the website since they can't see availability on their system.