Locked out of phone

[AC Question]

So I sold my Galaxy s6, I factory reset the phone but I did not realize that I had not removed the account(s) from the phone so the buyer is locked out, when I give him a login it does not work, he is just sent back to the screen telling him to enter the email.

 

[belodion]

Have you done everything here?:
http://m.androidcentral.com/factory-reset-protection-what-you-need-know