I have error 4000, iPhone 7 won't update

Thank you so much for this workaround.

I am having issues updating my iPhone 7 and iPad Air (3rd generation) since iOS14 came out.

Even did a reinstall of my iPad, but that has not solved the update issue.

Turning off Passcode temporarily solves the issue and now I can update again through iTunes.

Bug in iTunes unfortunately.

Either use WiFi instead or

Temporarily turn off Passcode on the phone and open the phone before connecting,

NB second option will delete the cards from Apple Pay wallet.

You’re welcome. Glad it solved the current situation with the workaround but we do keep reminding the hosts of the problem !