After a visit has been booked you can add additional medical services. Use this endpoint to add new medical services to the visit. You can do this until the visit's date time minus the lead time configured for your account (typically 24-48 hours).
Visits do now allow duplicate medical services
Visits require at least 1 medical service
If you add a service for 1 patient on the visit, you are adding that service for every other patient on the visit