code: protected int addPayload(RequestBuilder builder, String payload) {
      if (payload == null || payload.length() == 0) {
        return 0;
      }
  
  
      builder.setHeader(HttpHeaders.CONTENT_TYPE, contentType.getMimeType());
      builder.setEntity(new StringEntity(payload, contentType));
      return payload.length();
    }
docs: Add payload to request. By default, payload is sent as application/json