Reset FF3+ fails due to google account

Hi, we resetted a ff3+ to factory with hard reset. After rebooting it asks for the google account the phone was syncronized with.
The original customer comes in and entered his data. Email and password. Phone asks who will use this phone? we checked me/myself and then the same form comes up again to fill in email and password. It cycles all around.
We checked the password by login in to google account on a pc and this works, password is ok.
What can we do?
Thanks and best regards, Michael

Can you reset the FP3 without a SIM or SD card and then skip the Google account, then add SIM etc.

@Lengen1971

Is this resource of any help to you getting around this?
https://www.youtube.com/watch?v=vRE0bzIe1ac

thanks a lot, will check this out.