Upgrade I-cloud
Can I use my I-tune account to upgrade my I-cloud account?
And how would I do it?
iPhone SE, iOS 14
Click on this link to discover how to "Upgrade your iCloud storage plan" --> https://support.apple.com/HT201318
To learn 'What you can buy with your Apple ID balance'
click here --> https://support.apple.com/HT211187
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iCloud
Pay for iCloud storage.
So yes, the funds you have to pay for items from the iTunes Store can also be used to pay for iCloud storage.