iPad Air 2 still cannot update install what happen?

Hello,

Here's two different ways to ensure the highest iOS that your device will support is on your device.

Update your iPad wirelessly. Click here --> Update your iPhone or iPad - Apple Support

Here are instructions about how to update your iPad with the Finder on a Mac computer --> Update your iPhone, iPad, or iPod touch with the Finder - Apple Support

Your iPad air should update to 15.7.3.