Creates a new email schedule for existing email template. Email template can be scheduled based on two parameters: reservationStatusChange and reservationEvent. Only one of the parameters can be used. reservationStatusChange schedules email to be sent when reservation status transitions to a specific one, for instance: confirmed. reservationEvent schedules email to be sent number of days prior or after a specific event, for instance: after_check_out at a given time This call is only available for third-party integration partners, and not for property client IDs.