Extract customer info on appointments with maximum number of attendees higher than 1 with Graph API

Hi, is there a way to extract customers information with Booking Graph API (or other means) from an appointment configured with multiple attendees? When the service is configured with only one attendee I have the customer info, but with multiple attendees, there is no information returned by Graph (should be presented as an array of customers). Also I'm unable to extract custom fields in any situations.

I'm using Booking Graph API : 

Ex: https://graph.microsoft.com/beta/bookingBusinesses/DemoBooking@contosos.com/appointments/[Id]

Thanks.