@Gwave

Relplace OnStart Function with this one below

protected override void OnStart()
        {
            ServicePointManager.Expect100Continue = true;
            ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12;

            // If you didn't set a channel, then find channels by looking at the updates
            if (string.IsNullOrEmpty(ChannelId))
            {
                _telegramChannels = ParseChannels(GetBotUpdates());
            }
            else
            {
                _telegramChannels.Add(ChannelId);
            }
            SendMessageToAllChannels("Hellow world.. ");

        }

if u r using visual studio , you get error line under Tls12, just ignore it as it works when u build in CTrader.

It will fix the code for you