AMRestoreErrorDomain error 6 - failed to fixup var

From > Get help with iOS update and restore errors - Apple Support

Check your security software

Related errors: 2, 4, 6, 9, 1611, 9006. Sometimes security software can stop your device from communicating with either the Apple update server or with your device.

Check your security software and settings to make sure that they aren't blocking a connection to the Apple servers.

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On what Mac or mobile device, with what operating system?

on I phone 6 plus

the massage was " the I phone could not be restored . an unknown error occurred (6) "