Happened to me recently. There were two tickets. I tried to book 1. Payment rejected. Tried a different payment method and got the spinning wheel. Checked and it did not confirm. Tried to rebook and there was only 1 seat showing. I was able to book it using a different payment method. Out of curiosity, I checked to see whether the 1 seat would show back up and it did between 30 and 90 minutes later.