while updating ipad through my itunes i get an unknown error 4000

See >>> If you see an error when you update or restore your iPhone, iPad, or iPod - Apple Support

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 Get 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

I ran into this same problem. I was able to work around the problem by doing this:

1. In iTunes, hold down the shift key and then click the "Update" button
2. Go to C:\Users\seitz\AppData\Roaming\Apple Computer\iTunes\iPhone Software Updates
3. Select ".ipsw" file

My iPhone update then completed successfully.