I can’t back up my iCloud

when the message is not enough storage

See -> If you can't back up to iCloud -> If you can't back up to iCloud - Apple Support

• 👉 Upgrade your iCloud+ plan to get more space

See also the following Apple articles:

Upgrade to iCloud+ -> Upgrade to iCloud+ - Apple Support

iCloud+ plans and pricing -> iCloud+ plans and pricing - Apple Support

How to use iCloud on iPhone -> How to use iCloud on iPhone – Apple Support (UK)

Manage your iCloud storage -> Manage your iCloud storage - Apple Support

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You can also back up to your computer, and yes, you need to have enough space on your computer.

Aee -> How to back up your iPhone, iPad, and iPod touch

How to back up your iPhone, iPad, and iPod touch - Apple Support