Multiuserchat InvitationListener Smack: 4.1.0 not getting called

Question

I have already gone through related questions on stack but all in vain. I am not getting callback in Invitation Listener. Any help will be appreciated.

MultiUserChatListener

 MultiUserChatManager.getInstanceFor(connection).addInvitationListener(new InvitationListener() {
        @Override
        public void invitationReceived(XMPPConnection conn, MultiUserChat room, String inviter, String reason, String password, Message message) {
            String nickname = AppSharedPereference.getInstance(mContext).getUserName();
            try {
                mchat.join(nickname);
            } catch (SmackException.NoResponseException e) {
                e.printStackTrace();
            } catch (XMPPException.XMPPErrorException e) {
                e.printStackTrace();
            } catch (SmackException.NotConnectedException e) {
                e.printStackTrace();
            }
        }
    });

}

sendInvitation Method

public void sendInvites(ArrayList<ContactData.Usercontactsdetail> usercontactsdetail) {
            try {
                for (int i = 0; i < usercontactsdetail.size(); i++) {
                    String userID = usercontactsdetail.get(i).getContactid();
                    String user = userID + "@" + connection.getHost();
                    mchat.invite(user,
                            userID + "_user");
                }
            } catch (SmackException.NotConnectedException e) {
                e.printStackTrace();
            }finally {
                usercontactsdetail = null;
            }
        try {
            mchat.sendMessage("New group created");
        } catch (SmackException.NotConnectedException e1) {
            e1.printStackTrace();
        }
    }