error mesasge 4013 on iphone 6s

I have no idea what you saw on the Apple website, but this is the link for that issue-->If you see error 9, 4005, 4013, or 4014 when you restore your iOS device - Apple Support. Note that you must have iTunes version 12.8 or later. So just checking for the "latest version" is not good enough; the iTunes update will update to the latest version compatible with your operating system, which may not be 12.8.

And note that the last step is to contact Apple support. That is the link at the top of this page or the link in Apple's tip above, not this user-to-user forum.