How to set the Outlook Email Sensitivity using API Call ?

Trying to set the sensitivity of an outbound Email using following API. No error. Email is sent/received successfully. But Message sensitivity is NOT set to "Secure" as expected. Pls help.

{

  "message": {

    "subject": "Mail API Test",

    "body": {

      "contentType": "Text",

      "content": "Mail API TestMail API Test."

    },

    "toRecipients": [

      {

        "emailAddress": {

          "address": "*** Email address is removed for privacy ***"

        }

      }

    ],

    "ccRecipients": [

      {

        "emailAddress": {

          "address": "*** Email address is removed for privacy ***"

        }

      }

    ]

  },

  "singleValueExtendedProperties": [

            {

                "Id": "Integer 0x0036",

                "Value": "3"  

            }

        ]

}