docs: private String buildStartMessage(SynthesizeOptions options) {
      Gson gson = new GsonBuilder()
          .setFieldNamingPolicy(FieldNamingPolicy.LOWER_CASE_WITH_UNDERSCORES)
          .create();
      JsonObject startMessage = new JsonParser()
          .parse(gson.toJson(options))
          .getAsJsonObject();
  
      // remove options that are already in query string
      startMessage.remove(VOICE);
      startMessage.remove(CUSTOMIZATION_ID);
  
      startMessage.addProperty(ACTION, START);
      return startMessage.toString();
    }