Chosen Solution
my iphone cant recover on i tunes gives error 21
I had a similar problem. I got an error 9 when updating to iOS 11 using iTunes. I updated my itunes, checked my usb cable and also tried another computer, but still the same problem. Finally I bypass the error and restored my iPhone with imyfone ios system recovery. It was recommended by my friend and it is really easy to use. Maybe you can have a try. Good luck!
