Create Meeting v2 API - add attendees / participants

I am running into this issue!

I have a PRO account.

I have created a meeting with the following settings
type of 2 (scheduled).
approval_type 1 (manually approve)
registration_type 2 (must register for each occurrence).

When I attempt to add a registrant to the meeting… I get a 200 success… but the body of the response is NULL!

Did i set my meeting up incorrectly?