iTunes cites Error 4000. But there is no error 4000 in the Apple listing...

See If you can't update or restore your iPhone, iPad, or iPod touch - Apple Support. If you're trying to update using iTunes try over the air instead, or vice versa.

Note if you're getting a -4000 error when updating from iTunes you need to disable Find My iPhone, update, then enable again afterwards.

tt2

Ah, that sounds like a slightly more efficient workaround.

tt2