take a look at this post from last week or the week before:  https://community.intersystems.com/post/how-create-business-service-read...

Class TMP.AppointmentReqMsg Extends Ens.Request
{ // ProcessingFlag property is used to determine if the appt is for Cerner, Cerner and VistA or just VistA. // This flag is used by the BP Property ProcessingFlag As %String; Property MessageId As %String; Property ControlId As %String; Property LogicAppRunId As %String(MAXLEN = 150); Property AppointmentID As %String(MAXLEN = 150); Property AppointmentType As %String; Property StartTime As %String; Property Duration As %String; Property VisitStatus As %String; Property CancelCode As %String; Property CancelReason As %String; Property CancelRemarks As %String(MAXLEN = 160); Property ClinicallyIndicatedDate As %String; Property Comments As %String(MAXLEN = 160); Property VvdUrl As %String(MAXLEN = 500); Property SchedulerInfo As array Of SchedulerInfo; Property PatientInfo As TMP.PatientInfo; Property ProviderFacility As %String; Property PatientFacility As %String; // Property PatientResources As list Of AppointmentResources; Property PatientResources As TMP.AppointmentResources; Property ProviderResources As TMP.AppointmentResources;

this is one of my classes to define a JSON message