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Make sure everything was done as was instructed in this document What to do before you sell, give away, or trade in your Mac - Apple Support

It would also help if you provided the exact error message. Right now I am guessing the Mac still has the settings from the previous owner and you need to basically erase the whole computer and start fresh.

Are you sure you're entering your Apple ID password correctly? Nothing like a caps lock key pressed down? Can you log into iCloud.com using this password just to make sure it is working?

Did you completely erase the computer? "Reset" to me does not mean that was what was done.

It might help if you just tell us what it says. I tried enlarging the image and just got fuzz as well as crick in my neck. ;-)

Another option:

Contact Apple. Click here --> Choose your country or region - Official Apple Support Select your country, then a product. If you don't see one that handles your issue then keep experimenting with selections until you reach one that gets you a chat session or a telephone call and get the representative to redirect you.

or:

Contact Apple for support and service --> "See a list of Apple phone numbers around the world."

Click here --> Contact Apple for support and service - Apple Support