How to fix the device could not be restored − An unknown error occurred (9) iTunes error (Nothing else worked)

The lightning cable is made of a few small wires attached to the lightning port. Over time and use, especially improper use, the cable grows weaker, to the point when one of the wires gets cut from the inside. In this case, there is nothing else you can do, but to replace the cable. Consider this solution, if you tried all the solutions, but none of them worked, and you have ensured that both your iOS device and computer function properly.

If none of the other solutions to fix iTunes error 9 worked, try restoring your device from another computer, as your computer, for some reason rejects your iOS device. Do this once you verify that the lightning cable works, and iTunes is up to date.

Note: You may need to take your computer to a repair shop, because it may have motherboard, or software issues.

If the traditional restoring fails, iOS devices have another mode for restoring, known as DFU (Device Firmware Update) more. Consider restoring your device through the DFU mode as a last resort, as it involves data loss, and only after you have verified that there is nothing wrong with your USB lightning cable and the computer. The procedure you need to follow is described below:

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

Note: If you use a laptop, 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.