Error installing iOS 15.7.9 on iPad Air 2. "Unable to install update"

Having downloaded an update, you are normally offered the opportunity to install now, or later. If you select the latter, you have deferred the install for automatic installation during "quite hours".

If you restart your ipad - and revisit the Software Update page in settings - you may be able to install immediately.

I have same issue... I downloaded upgrade few times, each time I got message unable to install

I have the same issue, have been trying for months to update.

And it does not say what is wrong or how to fix it.

You're very welcome.

How to download the ios15.8 
update

How can I download iOS15.8