I cannot subscribe to add storage to my iPhone

Read this support article for instructions on how to upgrade to iCloud+ --> Upgrade to iCloud+ - Apple Support

If you see an error message, we need to know what it says exactly in order to be able to help you.

Click on this link to find out how to sign in with your Apple ID --> Sign in with your Apple ID - Apple Support "After you log in, you can use the App Store, iCloud, iMessage, Apple Music, Apple TV+, and more."