Connect to Bankinter
Once connected, if you are on the website go to "Buy Amazon Gift Card" in the Services menu, or in the app open the menu, press "For being Bankinter" and then "Buy Amazon Gift Card".
Select the account and the amount
Select the account which you want to use to pay for the voucher and its amount.
Confirm the transaction and... done!
Confirm the transaction with the password sent to your phone. You will then get the code for your Amazon.es gift card on the screen.