Sold my watch after resetting it but the person says it is locked

Hi guys

I sold my Apple Watch Series 4 on Ebay this week, I did a factory reset like I've done with all my devices I've sold in the past.

The person has messaged me with screenshots showing the Apple watch requires my login for some reason.

I looked online and did an erase request on iCloud but he's saying he still can't get into it

What can I do?