Invalid Serial Number?

RayBeller wrote:

I have a valid MacBook Pro (Late 2012) and when I try and use the serial number, for instance, trade in value, it barks at me saying this... any ideas?

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reference— https://support.apple.com/my-support

if you still have an issue—

Update your proof of purchase

Contact Apple Support to update your Apple device information.

https://support.apple.com/en-us/HT202703

I can say that a mid-2012 15" MBP (non-retina) trade in with everything working—would be ~$220 USD

You may be better off selling it locally...