Error code

iOS 14

IOS14
System Error Code· A POSIX/system errno returned when a system call fails.

What it means

Communication error during restore — the device connection was lost and the IPSW could not be fully written..

How to fix it

  1. Delete the partially downloaded IPSW from ~/Library/iTunes/iPhone Software Updates (macOS) or C:\Users\<name>\AppData\Roaming\Apple Computer\iTunes (Windows) and re-download.
  2. Use a different cable and direct USB port.
  3. Ensure the computer has at least 10 GB of free disk space.
  4. Try the restore on a different computer.

Not affiliated with iOS. Answer summarized from the manufacturer's manual linked above; consult that source for the authoritative procedure.