Hello gulia162,
Thanks for using the Apple Support Communities. We understand that you're running into an issue redeeming an Apple gift card using your Android device. Did you follow the direction provided in article, How to redeem your Apple Gift Card or App Store & iTunes gift card, under section: Redeem a gift card on your Android device?
If so, and you're not seeing the option, there are couple things you can try.
- Make sure the app is updated
- Quit the app, restart your device, and relaunch the app
- Delete and reinstall
If you continue to experience issues, feel free to reach out to Apple Support for additional assistance at Get Support.
Best regards.