TRTH Historical Criteria search

I am trying to retrieve all stocks associated with Shanghai exchange using the historical criteria call for TRTH. The exchange code for Shanghai is SHH, when I put this into a call such as:

POST: https://hosted.datascopeapi.reuters.com/RestApi/v1/Search/HistoricalCriteriaSearch

{
  "Request": {
    "RicPattern": null,
    "BondTypeCodes": null,
    "ContributorIds": null,
    "CountryCodes": null,
    "CurrencyCodes": null,
    "ExchangeCodes": "SHH",
    "FutureMonthCodes": null,
    "InstrumentTypeCodes": null,
    "OptionMonthCodes": null,
    "OptionTypeCodes": null,
    "CouponRate": null,
    "StrikePrice": null,
    "ExpiryDate": null,
    "MaturityDate": null,
    "Range": {
      "Start": "2019-12-16T00:00:00.000Z",
      "End": "2019-12-17T00:00:00.000Z"
    }
  }
}

I get the following error:

{
"error": {
"message": "Malformed request payload: Invalid cast exception for property ExchangeCodes: Unable to cast object of type 'System.String' to type 'System.Collections.Generic.List`1[System.String]'."
}
}

CAn you confirm if I'm doing something wrong?