updating itunes on pc
An unknow error occured 4000 error
iPhone 11, iOS 14
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Presumably you're trying to update iOS not iTunes. The workaround for this error is to disable Find My iPhone on the device before tying to update with iTunes for Windows.
For general update problems see If you can't update or restore your iPhone, iPad, or iPod touch - Apple Support. If you're trying to update over the air try using iTunes instead, or vice versa.
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