Says I don’t have enough storage for an update but I do

Your iPad is telling you don't have enough free storage to update your iPad because you don't have enough free storage to your iPad.

To update your iPad, your iPad needs enough storage to both a) download the update and b) unpack and install the update. If you need 4 GB of storage to download the update, and at least 4 GB more to install the update, you need 8 GB+ free in total.

Your device has likely already told you what you need to do – following your iPad's storage tips can help you install a new update. Try:

• Offloading apps you haven't used in a while. Offloading keeps your data while deleting the application. You can reinstall the app at any time from the App Store
• Reviewing large message attachments. Photos and videos you've received in iMessage from a long time ago may be taking up more storage on your device than you realize.
• Deleting local copies of music & TV shows. Music, TV shows, and movies take up large amounts of storage. If you can stream a song later, or redownload your favorite show later, you may want to delete the copy now to free up some space.
• Optimizing photo storage. Your iPad may have local copies saved of every photo and video you have, eating up all of your storage. Turn on "Optimize iPhone Storage" to keep the full-quality versions of your photos in iCloud instead.

Learn more:

If you need more space for an update on your iPhone, iPad, or iPod touch - Apple Support

Manage your photo and video storage - Apple Support

The general consensus, based upon many years of experience, is that you should aim to maintain at least 4-6GB of available free space for iPadOS to use for temporary storage.

This is particularly important when performing an OTA system software update - as there must be adequate free-space in which to download, unpack and verify an update prior to installation. As soon as the update has been successfully installed, the OS will automatically clean-up temporary files - releasing this space to the system as free-space. Major version updates require considerably more temporary space than smaller point-updates.

If you are short of space, you can selectively offload Apps. Offloading Apps removes just the Apps themselves - but preserves the associated App data and settings. Apps are typically only offloaded to provide additional temporary storage space - so as to perform a system software update where available storage in insufficient. Subsequent access will cause the offloaded App to automatically reinstall.

https://9to5mac.com/2020/01/21/how-to-offload-apps-in-ios-to-save-space-without-deleting-their-data/

By contrast, deleting an App from the iPad removes both the App and the associated user-data. Unless this data has been backed-up elsewhere, the associated data will be lost.

An alternative strategy where space is short is to perform the update using a Windows PC (with iTunes for Windows installed) or a Mac computer (with iTunes or Finder - as appropriate for the installed version of macOS) to perform the update. Here the update package is downloaded, unpacked and verified on the computer - before the update is installed by the computer on the target device. Notwithstanding the general recommendation to maintain at least 4-6GB of free-space on the iPad, this method requires considerably less free-space to successfully install an OS update on a space-constrained device.

Additional information about creating sufficient space for installation of a software update can be found here:

If you need more space for an update on your iPhone, iPad, or iPod touch - Apple Support

My wife’s iPad mini received this error and I freed up space until the device reported it had over 10 gb of free space. When I try to install the update, I get the same error. I’ve restarted the device to make sure there isn’t an issue with cached data getting in the way, but still can’t update. Any suggestions?