我的不和谐机器人是不发送任何消息时，我键入“！你好”，即使所有的在线文档应该是说，这是正确的，我遵循了教程，显示它的工作。有人能帮助我吗？
我使用的是discord.net3.8.1（目前最新版本）和dotnet sdk版本7.0.100

using Discord;
using Discord.WebSocket;
using System;
using System.IO;
using System.Threading.Tasks;

namespace discorddotnet
{
    class Program
    {
        public static void Main(string[] args)
        => new Program().MainAsync().GetAwaiter().GetResult();

        private DiscordSocketClient _client;
        public async Task MainAsync()
        {
            _client = new DiscordSocketClient();
            _client.MessageReceived += CommandHandler;
            _client.Log += Log;

            //  You can assign your bot token to a string, and pass that in to connect.
            //  This is, however, insecure, particularly if you plan to have your code hosted in a public repository.
            var token = File.ReadAllText("token.json");

            // Some alternative options would be to keep your token in an Environment Variable or a standalone file.
            // var token = Environment.GetEnvironmentVariable("NameOfYourEnvironmentVariable");
            // var token = File.ReadAllText("token.txt");
            // var token = JsonConvert.DeserializeObject<AConfigurationClass>(File.ReadAllText("config.json")).Token;

            await _client.LoginAsync(TokenType.Bot, token);
            await _client.StartAsync();

            // Block this task until the program is closed.
            await Task.Delay(-1);
        }

        private Task Log(LogMessage msg)
        {
            Console.WriteLine(msg.ToString());
            return Task.CompletedTask;
        }

        private Task CommandHandler(SocketMessage message)
        {
            //variables
            string command = "";
            int lengthOfCommand = -1;

            //filtering messages begin here
            if (!message.Content.StartsWith('!')) //This is your prefix
                return Task.CompletedTask;

            if (message.Author.IsBot) //This ignores all commands from bots
                return Task.CompletedTask;

            if (message.Content.Contains(' '))
                lengthOfCommand = message.Content.IndexOf(' ');
            else
                lengthOfCommand = message.Content.Length;

            command = message.Content.Substring(1, lengthOfCommand - 1).ToLower();

            //Commands begin here
            if (command.Equals("hello"))
            {
                message.Channel.SendMessageAsync($@"Hello {message.Author.Mention}");
            }

            return Task.CompletedTask;
        }
    }
}