The website sometimes doesn't work for no apparent reason. In this case, call the contact center and they should be able to make the booking for you over the phone, assuming the award is still available. I have to warn you though, actual ticketing requires a separate department to email you a payment link, and last time I did that they f***ed up and didn't ticket it even when I paid. It was a pain in the *** to get it resolved. Good luck.