code: public String export(String downloadFormat, Map<String,String> headers) throws ServiceException {
          try {
              JsonExport exporter = getExporter(headers);
              if (Listener.DOWNLOAD_FORMAT_EXCEL.equals(downloadFormat))
                  return exporter.exportXlsxBase64();
              else if (Listener.DOWNLOAD_FORMAT_ZIP.equals(downloadFormat))
                  return exporter.exportZipBase64();
              else
                  throw new ServiceException(HTTP_400_BAD_REQUEST, "Unsupported download format: " + downloadFormat);
          }
          catch (ServiceException ex) {
              throw ex;
          }
          catch (Exception ex) {
              throw new ServiceException(HTTP_500_INTERNAL_ERROR, ex.getMessage(), ex);
          }
      }
docs: Binary content must be Base64 encoded for API compatibility.