{
  "Subject": "TestSubject",
  "Body": "TestBody",
  "PreferredLanguage": "en-US",
  "Recipients": [
    {
      "FirstName": "TestName",
      "EmailAddress": "TestEmail"
    }
  ]
}

request.post(
        'https://someURL.com/messages',
        {
            json:
            {
                Subject: "TestSubject",
                Body: "TestBody",
                PreferredLanguage: "en-US",
                Recipients: [
                    {
                        FirstName: "TestName",
                        EmailAddress: "TestEmail"
                    }
                ]
            }
        }
    )