Re: iphone 5c with water damage
Put the iPhone in DFU mode, if you don't know how to do that, plug the phone to your computer and open up iTunes, then turn off the phone. Now hold down power on/off button and the home button for about 8 or 9s and release the power on/off button while keeping down the home button until iTunes recognize your phone in recovery mode. Note that the screen should be dark with nothing on it when iTunes recognize it and ask you to factory restore it. (You can do soMe google about how to enter DFU mode) Then follow on screen instruction to reinstall the latest ios into the device.
Also make sure that iTunes is communicating with the server, error 21 is when something like firewall or else preventing iTunes to communicate with the Apple server, connect to internet and check if you can access the iTunes Store in the the iTunes software or not, if no, then disable restrictions of iTunes in firewall if you ever enable it. It should work fine
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