Is this an iTunes gift card you are referring to? If so, make sure you've redeemed the iTunes gift card balance then this can be used to pay for your iCloud storage.
This thread has been closed by the system or the community team.
You may vote for any posts you find helpful, or search the Community for additional answers.
Use iCloud balance
Welcome to Apple Support Community
A forum where Apple customers help each other with their products. Get started with your Apple Account.