How can I use my iTunes gift card to pay for iCloud storage upgrades
How to use iTunes gift card to pay for iCloud storage upgrade and future payments
iPad 2 Wi-Fi + 3G, iOS 10.2
iCloud storage plans and pricing - Apple Support
"Accepted payment methods for iCloud storage upgrades include credit cards, debit cards, and iTunes Store credit. If you don't have enough iTunes store credit to complete your upgrade, you'll be charged the remaining amount. "