If you were trying to "Retain User's Data," switch to Quick Flash Mode to perform a clean install. This is often necessary if the error message mentions "Missing data volume".

ERROR: Unable to restore iDevice(-75). - Apple Community

Sometimes, Error -75 can be triggered if your computer cannot reach Apple's verification servers (gs.apple.com). This often happens if you have used software to block iOS updates or if you have modified your network settings.

Data corruption within the device's internal storage can prevent it from accepting new firmware. How to Fix Error -75 in 3uTools

: If the standard Recovery Mode fails, put the device into DFU mode before attempting the flash again.

Disconnect your device. Right-click -> Manage -> Device Manager .

: Download the firmware directly from IPSW.me, then use the "Import" button in 3uTools to select that specific file for the restore.

The flash process requires stable power. If the battery is old or damaged, the restore may fail, with some users reporting that 3uTools verifies battery health during the restore.