Why is it saying that I can’t backup

The most common reason one can't do an iCloud backup is they don't have enough space in iCloud. When you open an iCloud account, you get 5gb of storage at no charge. At some point, that amount of space gets used and if you want to continue to use iCloud backup, you'll have to invest in buying more storage. You can buy 50gb of storage for $1/month - $12/year.

Here is a link about hot to add more iCloud storage --> iCloud+ plans and pricing - Apple Support

aleigha2012 Said:

"Why is it saying that I can’t backup: Why is it saying that a can’t do backup???? so can you till me please so"

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Please Provide More:

What exactly is the device are you back up? What update are you looking to install? Note: You cannot backup everything to iCloud. Learn about this here: What does iCloud Back Up? - Apple Support