How to fix an unknown error occurred (1671) in iTunes (Nothing else worked)

You can restore your device from DFU (Device Firmware Update) mode, but only as a last resort, as it involves data loss, only if you have verified that there is nothing wrong with your device's lightning port, USB lightning cable and the computer. Follow the procedure described below, to restore your device via the DFU mode:

1. Put your device into DFU mode - consult this article on Apple, if you are not sure how;
2. Connect your device to your computer, through the USB lightning cable;
3. Restore your device, following the on-screen instructions on your computer.
   
   

Note: If you use a laptop to restore your device, make sure to plug it in the power adapter first, as interrupting the restoring process is not advised and can be dangerous for your device.

Consider resetting your device as a last option, if you tried all the other solutions to fix error 1671, but none of them worked. Maybe the root of the error is deeply entrenched into vital operating system files that resetting your device is the only option left.

To reset your device:

1. Go to Settings, tap on General and select Reset;
   
      
   
   
   
2. Tap on Erase All Content and Settings, select Erase iPhone (iPad/iPod)
3. Enter your passcode, and select Erase;