It seems like when saving Influencer it is trying to create a new record - and if Influencer is derived from User - then you are missing email, username, etc.

I think what would work is after committing the User record - re-read it back as the appropriate type (Influencer/Sponsor) - then fill in additional params.

I am not sure why you can’t just create an Influencer/Sponsor record in full at registration time rather than the 2-step process.. I must be missing something.