How can I use my gift card for the iPhone 14?

Hi everyone, I would like to know how can I use my gift card for the iPhone 14 $799 I'm already getting angry it show on the App Store $150 remaining but when I go to my cart it show $854 total but I don't see anywhere that show use gift card or even add gift card I'm on my MacBook apple website and I don't see it anywhere.

[Re-Titled by Moderator]