I would make sure you have enough on your card for the total cost x 2. So if it was $250, you ought to have $500. The reason is, Debit cards are, well, they are money, while credit cards are credit. When Apple Pre-Authd your card, it put a pending charge on your card that WILL go away, but that money is still unavaliable, so if Apple charges for the final shipment and that previous authorization has not fallen off yet, both of those charges will take away from your balance. If you have enough money, there is nothing to worry about. Its really best to use Credit Cards, even if you buy it and pay it off the same month, debit is just too risky.