[AmandaFrier8]

I updated my iPhone 7 (Verizon) to IOS 11 Public Beta 4 and had it for a short time, but recently decided to downgrade back to IOS 10.3.3 using a backup on itunes. It got stuck and eventually fails at about 60 percent and gave me a popup with an error saying:

"The iPhone "iPhone" could not be updated. An unknown error occurred (-1)."

I tried both Restore and Update on itunes and got the same result. I tried wiping it completely using an ipsw (IOS 10.3.3) and even that didn't do the trick.

The iPhone boots to the Apple logo then goes directly to Recovery Mode.

I'm a bit stuck here, what should I do?

[Ariel Babalao]

1- Update your iTunes version. Is installation still fail then do step 2.
2- Disconnect other USB cables from the computer and leave only the iPhone connected to it. If still given error then do step 3.
3- Turn off your antivirus or such and reboot your computer making sure that antivirus will remain inactive after reboot.

That should help solve the error issue in most cases.

[Just_Me_D]

Download and install the latest iTunes version. If you haven’t already. Reboot your cable/DSL modem, your router and your computer. Put your iOS device in DFU mode, connect it to your computer, and when iTunes detect that it’s in recovery, select to restore and update.

[AmandaFrier8]

@Ariel Babalao @Just_Me_D

I have tried the methods you both listed and I'm getting the same results, sadly. I can go into recovery mode but can't seem to get into DFU mode.

Edit: I can get into DFU mode, but I have the same result. I seen that my error code (-1) seems to be a hardware issue.

I'm stuck, I have seen some "fixes" online where people heat up the back of the phone then immediately try the restore process again.

Anything else? :-/

[TripleOne]

This happened to me out of nowhere and it shocked me. I then replaced my lightning cable with another one, and after that it restored the iPhone just fine!