Http response: Cannot convert JSON into stream

Question

I have an API in JAVA to upload a zip file to a server in Delphi, and I am doing it as follows:

        DSRESTConnection conn = new DSRESTConnection();
        conn.setHost("example.com");
        conn.setPort(8080);
        TServerMethods1 proxy = new TServerMethods1(conn);
        try {
            ByteArrayOutputStream baos = new ByteArrayOutputStream();
            BufferedOutputStream bos = new BufferedOutputStream(baos);
            ZipOutputStream zos = new ZipOutputStream(bos);
            zos.putNextEntry(new ZipEntry("test.json"));
            byte[] bytes = inputJson.getBytes();
            zos.write(bytes, 0, bytes.length);
            zos.close();
            bos.close();
            baos.close();
            TStream outZip = new TStream(baos.toByteArray());

            zipResponse = proxy.UserZipUpLoad("username", "password", 5, outZip, outZip.asByteArray().length);
        } catch (DBXException | IOException e) {
            e.printStackTrace();
        }

and here is the API:

    public UserZipUpLoadReturns UserZipUpLoad(String user, String pwd, int ZipType, TStream strmUpLoad, long iSize) throws DBXException {
  DSRESTCommand cmd = getConnection().CreateCommand();
  cmd.setRequestType(DSHTTPRequestType.POST);
  cmd.setText("TServerMethods1.UserZipUpLoad");
  cmd.prepare(get_TServerMethods1_UserZipUpLoad_Metadata());
  cmd.getParameter(0).getValue().SetAsString(user);
  cmd.getParameter(1).getValue().SetAsString(pwd);
  cmd.getParameter(2).getValue().SetAsInt32(ZipType);
  cmd.getParameter(3).getValue().SetAsStream(strmUpLoad);
  cmd.getParameter(4).getValue().SetAsInt64(iSize);
  getConnection().execute(cmd);
  UserZipUpLoadReturns ret = new UserZipUpLoadReturns();
  ret.ReturnCode = cmd.getParameter(5).getValue().GetAsInt32();
  ret.ReturnString = cmd.getParameter(6).getValue().GetAsString();
  ret.returnValue = cmd.getParameter(7).getValue().GetAsInt32();
  return ret;
}

To create the body for the request, _parameter is created of the params in the API which cannot be in the url such as a byteArray or blob:

boolean CanAddParamsToUrl = true;
        _parameters = new TJSONArray();
        for (DSRESTParameter parameter : ParametersToSend)
            if (CanAddParamsToUrl && isURLParameter(parameter))
                URL += encodeURIComponent(parameter) + '/';
            else // add the json representation in the body
            {
                CanAddParamsToUrl = false;
                parameter.getValue().appendTo(_parameters);
            }

and using the _parameters, body is built:

TJSONObject body = new TJSONObject();
                body.addPairs("_parameters", _parameters);
                p.setEntity(new StringEntity(body.toString(), "utf-8"));

I don't have access to the server side and don't know what happens there. When I send a JSON object or any other strings, the server returns ok but as soon as I zip the JSON and send it, the server return error 500 saying "Cannot convert input JSON into a stream". I think the JSON it is referring is the body not the JSON string in the file.

From the last part of the code I can see why a string would work but I don't know how to use the current code to send a zip file as requested. Is there anyway to use this code? or should I change it? If so, how? Does anybody know if this is a bug?