Lots of worriers here. It is only a graphics card lol.
My experience was that once you've added it to your cart, you get some time to finish the order.
2nd thing is checking payment details, address and probably ip address too. This is generally where it goes wrong (tried to buy another FE a while go, but didn't change details), so should be good if payment is accepted.
In hindsight, I wonder if I could have brought one today from my phone's 4G connection, even though I'm on Three's 200mb free data sim package... would've needed my login details to hand though.
Does anyone know if third party payment methods like Wise (aka TransferWise) would be accepted to buy an FE card? Its a Mastercard (debit) so in theory, this should work.