Cannot update Ipad Air 2

This support page makes reference to 4000-series errors:

If you see error 9, 4005, 4013 or 4014 when you restore your iOS device – Apple Support

Whilst Error #4000 is not explicitly listed in this support page, Apple Support are known to recommend that you follow these steps when troubleshooting this error - prior to seeking further assistance from Apple Support.

Apple Support can be contacted directly using the Contact Support link at top-right of this page - or by using the excellent Apple Support App. If the App is not already installed, it can be downloaded from the App Store:

https://apps.apple.com/gb/app/apple-support/id1130498044

If the information that you have received from LotusPilot, this is what I've experienced in the past. Error 4000 is a Windows and iTunes error. Until Apple updates iTunes, you will continue to receive the error if you attempt to update or restore your device in iTunes. A workaround for now is to temporarily disable the passcode on your device, update, then put the passcode back on. The con to this is that it will remove all of your credit cards in Apple Wallet. Another option is to go to Settings>General>Software Update and update from there.

mumser101 wrote:

I got it upgraded finally. It seems to be a cable issue. I think the first cable was for charging only, no data lines. By using another cable, the upgrade went smoothly.

Some cables are intentionally designed to support charging only - lacking data connection. Charge-only cables are often used to deliberately isolate a device from an “untrusted” USB port. Obviously, a charge-only cable is of no use when using a computer to transfer data and/or perform a software update of your device.

By isolating the USB data lines, the device to which you have connected cannot access your device. A common attack vector encountered in public areas (such as airports and transport hubs), apparently innocuous USB changing points may have been modified with embedded software that is designed to access or compromise devices that are connected. We have all been in situations where we need to recharge a device from an accessible USB outlet - and threat actors don’t miss this opportunity.

For information…

Infosec Professionals advise that you should never connect to a USB port unless you explicitly trust that it is safe. Keeping a charge-only cable for situations where you cannot avoid recharging your device in public settings is recommended for situations where you cannot be absolutely certain that the USB connection is safe. Better still, carry your own AC-powered Power Adapter, or a PowerBank when travelling.

What version of iPadOS is your iPad, currently, running?

How much free internal data storage space is “plenty” of space?

Your iPad needs to maintain, at the very least, 3-6 GBs, or greater, free internal data storage space.

Also, is your iPad running a beta version of iPadOS?

You would need to remove/uninstall this beta OS software before your iPad will be able to install the Apple officially released iPadOS 15.7.1.

All Apple mobile device cables are power/charging AND data transfer cables.

Even third party cables for mobile smart devices do all three things.

Perhaps your first cable is simply bad/faulty.

Glad you got it working.

Using iPad Air 2 update will not update 15.7.1plenty of space will not load.