You can get an unknown error or a '0xE' error if your computer doesn't recognise your connected device. Follow these procedures, and after each one, try to reconnect your device.

Make sure your iOS or iPadOS device is on the Home screen, powered on, and unlocked.

• Make sure your Mac or Windows PC has the most up-to-date software. Make sure you have the most recent version of iTunes if you're using it.
• Unlock your smartphone and tap Trust if you get a Trust this Computer alert. Find out what to do if you can't unlock your cellphone because you forgot your passcode.
• With the exception of your device, unplug all USB accessories from your computer. To see if any of the USB ports work, try them all. If that doesn't work, try an alternative Apple USB cable.
• Your computer should be restarted.
• Your iPhone, iPad, or iPod touch should be restarted.

Read More: How do I connect a memory stick from a camera, GPS or other device to a Mac?