code: public void leave(final Respoke.TaskCompletionListener completionListener) {
          if (isJoined()) {
              if ((null != groupID) && (groupID.length() > 0)) {
                  String urlEndpoint = "/v1/groups";
  
                  JSONArray groupList = new JSONArray();
                  groupList.put(groupID);
  
                  JSONObject data = new JSONObject();
                  try {
                      data.put("groups", groupList);
  
                      signalingChannel.sendRESTMessage("delete", urlEndpoint, data, new RespokeSignalingChannel.RESTListener() {
                          @Override
                          public void onSuccess(Object response) {
                              joined = false;
  
                              Respoke.postTaskSuccess(completionListener);
                          }
  
                          @Override
                          public void onError(final String errorMessage) {
                              Respoke.postTaskError(completionListener, errorMessage);
                          }
                      });
                  } catch (JSONException e) {
                      Respoke.postTaskError(completionListener, "Error encoding group list to json");
                  }
              } else {
                  Respoke.postTaskError(completionListener, "Group name must be specified");
              }
          } else {
              Respoke.postTaskError(completionListener, "Not a member of this group anymore.");
          }
      }
docs: Leave this group
  
  @param completionListener  A listener to receive a notification on the success of the asynchronous operation