A typical message header

{
  "resourceType": "MessageHeader",
  "id": "1cbdfb97-5859-48a4-8301-d54eab818d68",
  "text": {
    "status": "generated",
    "div": "<div xmlns=\"http://www.w3.org/1999/xhtml\">\n      <p>Update Person resource for Peter James CHALMERS (Jim), MRN: 12345 (Acme Healthcare)</p>\n    </div>"

  "resourceType" : "MessageHeader",
  "id" : "1cbdfb97-5859-48a4-8301-d54eab818d68",
  "text" : {
    "status" : "generated",
    "div" : "<div xmlns=\"http://www.w3.org/1999/xhtml\">\n\t\t\t<p>Update Person resource for Peter James CHALMERS (Jim), MRN: 12345 (Acme Healthcare)</p>\n\t\t</div>"

  },
  "eventCoding": {
    "system": "http://example.org/fhir/message-events",
    "code": "admin-notify"

  "eventCoding" : {
    "system" : "http://example.org/fhir/message-events",
    "code" : "admin-notify"

  },
  "destination": [
    {
      "name": "Acme Message Gateway",
      "target": {
        "reference": "Device/example"
      },
      "endpoint": "llp:10.11.12.14:5432",
      "receiver": {
        "reference": "http://acme.com/ehr/fhir/Practitioner/2323-33-4"
      }

  "destination" : [{
    "endpointUrl" : "llp:10.11.12.14:5432",
    "name" : "Acme Message Gateway",
    "receiver" : {
      "reference" : "http://acme.com/ehr/fhir/Practitioner/2323-33-4"

    }
  ],
  "sender": {
    "reference": "Organization/1"
  },
  "enterer": {
    "reference": "Practitioner/example"
  },
  "author": {
    "reference": "Practitioner/example"
  },
  "source": {
    "name": "Acme Central Patient Registry",
    "software": "FooBar Patient Manager",
    "version": "3.1.45.AABB",
    "contact": {
      "system": "phone",
      "value": "+1 (555) 123 4567"

  }],
  "source" : {
    "endpointUrl" : "llp:10.11.12.13:5432",
    "name" : "Acme Central Patient Registry",
    "software" : "FooBar Patient Manager",
    "version" : "3.1.45.AABB",
    "contact" : {
      "system" : "phone",
      "value" : "+1 (555) 123 4567"

    },
    "endpoint": "llp:10.11.12.13:5432"

    "sender" : {
      "reference" : "Organization/1"
    }

  },
  "reason": {
    "coding": [
      {
        "system": "http://terminology.hl7.org/CodeSystem/message-reasons-encounter",
        "code": "admit"
      }
    ]

  "reason" : {
    "coding" : [{
      "system" : "http://terminology.hl7.org/CodeSystem/message-reasons-encounter",
      "code" : "admit"
    }]

  },
  "response": {
    "identifier": "5015fe84-8e76-4526-89d8-44b322e8d4fb",
    "code": "ok"

  "response" : {
    "identifier" : {
      "value" : "5015fe84-8e76-4526-89d8-44b322e8d4fb"
    },
    "code" : "ok"

  },
  "focus": [
    {
      "reference": "Patient/example"
    }
  ],
  "definition": "http:////acme.com/ehr/fhir/messagedefinition/patientrequest"

  "focus" : [{
    "reference" : "Patient/example"
  }],
  "definition" : "http:////acme.com/ehr/fhir/messagedefinition/patientrequest"

}