I can’t pay by Gift card

The article "What type of gift card do I have?" explains the different kinds of gift cards Apple uses and has links on how to redeem them and what can be purchased with each kind. Click on the link --> What type of gift card do I have? - Apple Support

Read this support article to learn how to redeem your Apple Gift Card or App Store & iTunes gift card --> How to redeem your Apple Gift Card or App Store & iTunes gift card - Apple Support

Very similar to what is in this document:

If you can't redeem your Apple Gift Card or App Store & iTunes Gift Card read this document about things to try --> If you can't redeem your Apple Gift Card or App Store & iTunes Gift Card - Apple Support