I was changing one of my usual flights to an earlier time today, something I have done a few times before without issue. Admittedly, based on the cost of changing, availability was tight but I was surprised to see this message:
This came up after I'd just completed the Amex 3D Secure step, suggesting that until the credit card transaction is fully authorised, your seat isn't reserved.
Is it normal? I would have thought that once selected the seat is yours for 15 minutes to give you a chance to check out correctly.