American Express gift card online use

I'm pretty sure Amazon only charges your card when it ships. If it is an order confirmation, they haven't charged your card yet and they're merely confirming the details.

When I've bought stuff with an Amazon gift card that wasn't equal to the total, it uses up the gift card and then bills the rest to the card I have on file. I don't recall that it makes this particularly obvious, but then, the Amazon checkout process is a greased slope on purpose.

You could https://www.amazon.com/gp/help/contact-us/general-questions.html?ie=UTF8&skip=true to find out what you should do.

Is it possible you have another card already saved with Amazon?

Have you checked your email? Any time I've had a card declined (I have a few items on the Subscribe and Save plan, and sometimes I forget to put money on my debit card in time) they have always emailed me to tell me my payment didn't go through. I sincerely doubt they would just not send you the items without giving you a chance to straighten out the payment issues.

There's an order confirmation from Amazon that seems very standard. "We'd like to let you know that Amazon has received your order, and is preparing it for shipment. Your estimated delivery date is below." I do have other cards saved with Amazon, but I've never used or saved an Amex card. The order confirmation definitely says that it processed an Amex card with the last 4 digits that are my gift card.

Did you have any gift cards stored in your Amazon account? I've seen "also use £x.xx in gift cards" as a part of the checkout process, when I have some applied to my account.

If you have any other payment options stored on your Amazon account (gift cards, credits from previous returns/exchanges, a credit or debit card), they will use those to cover the balance that your Amex gift card did not cover. If you have no other payment options stored, then in the next few hours or days you'll receive an email from Amazon stating that your order is on hold because your payment method has failed, and it will indicate that you need to log into your account and update your payment info.

Not to my knowledge, no. There is 0.00 under Amazon gift cards, and the credit cards I have saved are just credit cards, not gift cards. (Conceivably they could have used one of the other credit cards, but I would have hoped they would have me approve that before doing so. There are two credit cards saved that I know about and actively use, and two old ones which I believe are the same account as one of the known ones, but were cancelled by me after losing them. I think. I very much hope an active confirmation by me to use one of the other accounts would have been necessary, because I'm not 100% sure what those two numbers are.)