C# How to get messages from channel/contact using Telegram API (not Bot API)

The provided link is old but it was a good starting point. Here is the updated working code:

 while (true)
            {
                var state = await _client.SendRequestAsync<TLState>(new TLRequestGetState());
                TrackingState = state.Pts.ToString();
                var req = new TLRequestGetDifference() { Date = state.Date, Pts = state.Pts-10, Qts = state.Qts };
                var diff = await _client.SendRequestAsync<TLAbsDifference>(req);
                var msgs = diff as TLDifference;
                if (msgs!=null && msgs.NewMessages.Count>0)
                {
                    var mss = msgs.NewMessages.Where(x => x.GetType() == typeof(TLMessage))
                        .Cast<TLMessage>().ToList().Where(x => x.Date > _lastMessageStamp && x.Out == false)
                        .OrderBy(dt => dt.Date);

                    foreach (TLMessage upd in mss)
                    {
                        Console.WriteLine("New message ({0}): {1}", upd.Date, upd.Message);
                    }
                    _lastMessageStamp = mss.Any() ? mss.Max(x => x.Date) : _lastMessageStamp;
                }
                await Task.Delay(2500);
            }