Simple Registration

I just want to use API to register my people, because i dont have an open course. but that does not work for now, so i made an registration formular via cluentCRM, but there it only works part of. a word-press-user gets created, but after registration i have to register again in fluenctcrm.? thats a little bit weird. i clicked on "automatically sign in via safe URL" or sth. like that, but it doesnt do it - therefore i come to the registration page, which is weird.

How did anyone who has a private community without open registrations solved this? is this not possible with FluentCommunity (without complex, double-registration and stuff like that).