Amazon.com does not allow you to use two payment options when paying for an item. But often, we wish to pay for part of a purchase using a gift card. The workaround is to use an Amazon online gift card for one part of the purchase.
Option  Buy an Amazon online gift card for the balance amount with your credit card (Amazon recommended method)
– Item price: $125
– Amazon online gift card: $25 (purchased using credit card)
– Pay balance with gift card: $100
Example: Gift card: $100. Item price: $125. Buy a $25 Amazon online gift card using your credit card. Add the Amazon online gift card to your Amazon account. During checkout, the $25 Amazon gift card balance will be automatically deducted. $125 item price – $25 Amazon gift card balance = $100 balance. Make the final payment with your $100 gift card. This option is recommended by Amazon – see email at the bottom of this post for details.
Option  Buy an Amazon online gift card with your gift card
– Item price: $125
– Amazon online gift card: $100 (purchased using gift card)
– Pay balance with credit card: $25
Example: Gift card: $100. Item price: $125. Buy a $100 Amazon online gift card using your gift card. Add the Amazon online gift card to your Amazon account. During checkout, the $100 Amazon gift card balance will be automatically deducted. $125 item price – $100 Amazon gift card balance = $100 balance. Make the final payment ($25) with your credit card.
Make sure you register your gift card so that you can use it for online shopping. Most gift cards will have a website listed on the back of the card which will provide additional information.
Email from Amazon customer service recommending option  above:
———- Forwarded message ———-
From: Amazon.com Customer Service
Date: Mon, Apr 6, 2009 at 11:12 PM
Subject: Your Amazon.com Inquiry
To: Bobby Maisnam
Thank you for writing to us at Amazon.com.
From your message, I understand that you want to use more than one payment method to pay for the item you want to purchase.
We cannot accept more than one payment method for an order on Amazon.com. Because gift cards issued by the major credit card companies also work exactly like credit cards, this restriction applies to those payment methods as well.
You can, however, combine Amazon Gift Cards with a credit, debit, or gift card issued by a major credit card company to complete your order.
If you wish, use your credit card to purchase an Amazon Gift Card for the amount that your credit card gift card balance will not cover and have it e-mailed to yourself. Then you can designate your credit card gift card as the payment method on the order and enter the Amazon Gift Card number in the Gift Card field of the order form.
We recommend that you do not use your credit card gift card to purchase an Amazon.com Gift Card. The authorization for the Amazon Gift Card purchase will actually decrease the amount immediately available for your order by $1.
We appreciate your business and look forward to your next visit to our store.
—- Original message: —-
Your Name:Bobby Maisnam
I have $157.99 in my cart ($119.70 + $25.20 + $13.09). I have a $100 visa debit gift card (Simon giftcard). How do I pay for the items in the cart using the gift card to pay $100 and pay the balance $57.99 with a debit/credit card?