Retrieving and Sorting Cases

I have an HTTP call that retrieves the cases associated with a specific AbEntry but I am trying add an OrderBy parameter but the results are still in ASC order.

{
  "Case": {
    "Scope": {
      "Fields": {
        "Key": 1,
        "CreationDate": 1,
        "CaseNumber": 1,
        "Reason": {
          "Key": 1,
          "Name": 1,
          "DisplayValue": 1
        },
        "Udf/$TYPEID(1782)": 1,
        "Udf/$TYPEID(1896)": 1
      }
    },
    "Criteria": {
      "SearchQuery": {
        "AbEntryKey": {
          "$EQ": "@{triggerBody()?['AbEntryKey']}"
        }
      }
    },
    "OrderBy": {
      "Fields": [
        {
          "CreationDate": "DESC"
        }
      ]
    }
  },
    "Configuration": {
        "Drivers": {
            "IAbEntrySearcher": "Maximizer.Model.Access.Sql.AbEntrySearcher"
        }
    }
}

My syntax is identical to the sample so why doesn't it work?