Tried to purchase a book, got message "couldn't process payment" What do we do?

Check the card details and expiry date via Manage your Kindle on Amazon.

Noretta,
Manage Your Fire & Kindle Payment Settings

1. Manage your content and Devices.
2. From Settings, select Edit Payment Method below Digital Payment Settings.
3. Select the desired credit card information, or add a new card, and then click Continue.
4. Enter the desired billing address, and then click Continue. You will be taken back to theDigital Payment Settings page where you can view your edited 1-Click payment method.

Follow the link below labeled "Help Search Results". It will take you to Amazons help site and give you the same instructions as above but will ask you to log into your account so you can actually do the above process without have to search around for the correct links.

Help Search Results

If you need further help, I’m available over the phone at https://www.6ya.com/expert/thomas_e8f475a8655f7b4a

1. Go to Manage Your Content and Devices.
2. From Settings, select Edit Payment Method below Kindle Payment Settings.
3. Select the desired credit card information, or add a new card, and then click Continue.
4. Enter the desired billing address, and then click Continue. You will be taken back to the Kindle Payment Settings page where you can view your edited 1-Click payment method.

http://www.amazon.com/gp/help/customer/display.html?nodeId=201252570

Hi
If you sign into your account and click on Help and then click "Go to Your Account", you get to a page with lots of links for various actions, then under Payment Methods, there is a link "Manage your Payment Methods". This will show you the cards that Amazon has registered to your account, and you can edit or delete the cards. On the previous page there is also a link to "Add a new card".This brings up a page where you can put in all the details for your new card. You can enter your details here, but they must exactly match the card details or it will be rejected when check with your card supplier.
Hope this is helpful, if so would you please register that with Fixya
Cheers

To redeem your gift card, go to the Amazon site and search for Gift Cards then click on"Apply a gift card to your account." . Find a claim code, on the card under grey protective coating and very gently scratch it off and reveal the claim code. Your purchases will be read in the "current Balance" and will remove the $ amount on your card, with each purchase. Enjoy spending!

You need to change the number on the Amazon site. Go to Amazon, your account, Manage payment options, will probably ask you to verify log in info, Click on Add payment method, You MUST set new card as default. That may be what you missed. I did it the last time I changed mine. There should be an option to delete old numbers.