The restore will usually go through without any problem.
Once you can get to the Home screen, go to Settings, General, About and look for the IMEI.
Just be sure that you have an active internet connection.
Solution 2: Check that your computer’s operating system is fully patched and up-to-date On a Mac, click Software Update from the Apple menu and install all available updates.
If you already know this tip, keep the link handy as a quick way to help a friend.“This i Phone could not be restored due to an unknown error (-1)” is probably one of the toughest one to fix because usually it is caused by hardware issues with your i Phone.