code: public boolean completeResponse(int surveyId, int responseId, LocalDateTime date) throws LimesurveyRCException {
          Map<String, String> responseData = new HashMap<>();
          responseData.put("submitdate", date.format(DateTimeFormatter.ISO_LOCAL_DATE) + " " + date.format(DateTimeFormatter.ISO_LOCAL_TIME));
          JsonElement result = updateResponse(surveyId, responseId, responseData);
  
          if (!result.getAsBoolean()) {
              throw new LimesurveyRCException(result.getAsString());
          }
  
          return true;
      }
docs: Complete a response.
  
  @param surveyId   the survey id of the survey you want to complete the response
  @param responseId the response id of the response you want to complete
  @param date       the date where the response will be completed (submitdate)
  @return true if the response was successfuly completed
  @throws LimesurveyRCException the limesurvey rc exception