ipad ios update 13.3.1 to 14.

I am trying to update my ipad (6th generation) using itunes on a windows pc (itunes version is current) and getting an error: Could not be updated. Unknown error (4000).

I have tried several things one at a time: 1. powered off/on 2. ipad set to be unlocked 3. turned off antivirus and powered off/on 4. powered off/on, changed USB cables and plugged directly into the computer. Nothing is working...any ideas? Thanks