Web Api: Add requiered people to an appointment

Hello,

Using the Web Api, I'm not able to add people to an appointment. I can create the appointment with a POST request to .../api/data/v8.2/appointments

{"scheduledstart":"2019-06-09T11:00:00Z","scheduledend":"2019-06-09T15:00:00Z","subject":"Appointment subject"
}

but no way to add "required people". I think I need to create something as an 'activityparties' but no success so far...

Has someone already did it ?

Thanks,

Danny