Presumably you have recently purchased a new device - and now see this in your device settings?

This is essentially a notification that Apple have provided you with the benefit of temporary additional iCloud storage with which to facilitate migration of your data from an existing Apple device to the new device that you have purchased.
This additional iCloud storage is used to create a full iCloud backup of your existing device. After creation of your new backup, this backup is kept available for 14-days prior to its deletion from Apple’s servers.
It would appear that this useful offer persists until such time as this temporary facility is used to create a backup. If you create the backup (which, incidentally, doesn’t have to be used after its creation), the banner will disappear - along with the temporary additional backup.