I want to add more space to iCloud

See the article Manage your iCloud storage - Apple Support

When you set up iCloud, you automatically get 5GB of storage. You can use that space for your iCloud backups, to keep your photos and videos stored in iCloud Photos, to keep your documents up to date in iCloud Drive, and more. You can always check how much iCloud storage you're using in Settings on your device or on iCloud.com. If you're running low, you can manage your storage to make more space or upgrade to iCloud+ any time.

Follow the instructions in the Related Article above. If you encounter a specific issue, describe it in this thread.

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