If you see the error message An unknown error has occurred (4013), it means that there was a problem updating or restoring your Apple device. Depending on the issue, this could be a relatively simple fix, but there’s always a chance that it points to a hardware problem. Read on to find out what causes iPhone error 4013 and seven ways to fix it.

This error, often called iPhone Error 4013, means that there is a problem restoring the iPhone from a backup or updating the operating system. It can affect the latest iPhone, older models, and the iPad and iPod touch.

You will know you are dealing with this error if you get the following message in iTunes:

This error is most often seen when the device disconnects from iTunes or when iTunes is unable to prompt the device to complete the update or restore process. In most cases, this is the result of a software error, but it can also be due to a hardware error, specifically the proximity sensor.