@arion the API does support signup types as a person or an organization. You just need to add an extra attribute called signup_type ans set is either to 0 for a person or 1 for an organization.

My question is different, I am asking to set the relations between a person and an organization to simulate the “Relationships” tab to assign “a person is a STUDENT AT an organization”. The form on that page has an endpoint “Relationships” that is not available for the current API version.