code: public ApiSuccessResponse singleStepConference(String id, SingleStepConferenceData singleStepConferenceData) throws ApiException {
          ApiResponse<ApiSuccessResponse> resp = singleStepConferenceWithHttpInfo(id, singleStepConferenceData);
          return resp.getData();
      }
docs: Create a conference in a single step
  Perform a single-step conference to the specified destination. This adds the destination to the existing call, creating a conference if necessary.
  @param id The connection ID of the call to conference. (required)
  @param singleStepConferenceData  (required)
  @return ApiSuccessResponse
  @throws ApiException If fail to call the API, e.g. server error or cannot deserialize the response body