code: public void singleStepConference(
              String connId,
              String destination,
              String location,
              KeyValueCollection userData,
              KeyValueCollection reasons,
              KeyValueCollection extensions
      ) throws WorkspaceApiException {
          try {
              VoicecallsidsinglestepconferenceData confData =
                      new VoicecallsidsinglestepconferenceData();
              confData.setDestination(destination);
              confData.setLocation(location);
              confData.setUserData(Util.toKVList(userData));
              confData.setReasons(Util.toKVList(reasons));
              confData.setExtensions(Util.toKVList(extensions));
              SingleStepConferenceData data = new SingleStepConferenceData();
              data.data(confData);
  
              ApiSuccessResponse response = this.voiceApi.singleStepConference(connId, data);
              throwIfNotOk("singleStepConference", response);
          } catch (ApiException e) {
              throw new WorkspaceApiException("singleStepConference failed", e);
          }
      }
docs: Perform a single-step conference to the specified destination. This adds the destination to the
  existing call, creating a conference if necessary.
  @param connId The connection ID of the call to conference.
  @param destination The number to add to the call.
  @param location Name of the remote location in the form of <SwitchName> or <T-ServerApplicationName>@<SwitchName>. This value is used by Workspace to set the location attribute for the corresponding T-Server requests. (optional)
  @param userData Key/value data to include with the call. (optional)
  @param reasons Information on causes for, and results of, actions taken by the user of the current DN. For details about reasons, refer to the [*Genesys Events and Models Reference Manual*](https://docs.genesys.com/Documentation/System/Current/GenEM/Reasons). (optional)
  @param extensions Media device/hardware reason codes and similar information. For details about extensions, refer to the [*Genesys Events and Models Reference Manual*](https://docs.genesys.com/Documentation/System/Current/GenEM/Extensions). (optional)