An interesting idea Maayan. My guess is that it would technically error out but you would still get the flight and you would pay for the miles which you don't receive!! My transaction did error out with a message to call Supporte, even though the flight reservation was made (I looked on checkmytrip; there was no email from LM until I called Supporte) and the full payment for the miles and the taxes went onto my credit card during the transaction. So one may end up with a negative balance and negative cash to match that !! But I'm not curious enough to try.