code: public ResponseWrapper addCrossFriends(String username, CrossFriendPayload payload)
              throws APIConnectionException, APIRequestException {
          return _crossAppClient.addCrossFriends(username, payload);
      }
docs: Add users from cross app.
  @param username Necessary
  @param payload CrossFriendPayload
  @return No content
  @throws APIConnectionException connect exception
  @throws APIRequestException request exception