I would recommend reaching out to our Media Solution Team and speak to the Samsung Account Department for further assistance on this. You can contact them by calling (855) 795-050.
I'm trying to setup my Note 4 for my son, and I'm having the same issue.
I did a master reset the Note 4.
It asked for my WiFi password. - Entered and connected
It them asked for my Samsung account User login and Password. - Process Failed
When I log on to my Samsung account on my PC it shows the Note 4 is still there.