Herord on Discord Bot youtube_dl和discord [voice]错误

Question

邮政编码：

import discord
import youtube_dl
from discord.ext import commands

client = commands.Bot(command_prefix = "e!")

players = {}

@client.event
async def on_ready():
    print("Bot çevrimiçi!")

@client.command(pass_context = True)
async def baglan(ctx):
    channel = ctx.message.author.voice.voice_channel
    await client.join_voice_channel(channel)

@client.command(pass_context = True)
async def oynat(ctx, url):
    server = ctx.message.server
    voice_client = client.voice_client_in(server)
    player = await voice_client.create_ytdl_player(url)
    players[server.id] = player
    player.start() 


client.run('')

错误：

packages/discord/ext/commands/core.py", line 54, in wrapped
        raise CommandInvokeError(e) from e
    discord.ext.commands.errors.CommandInvokeError: Command raised an exception: AttributeError: 'NoneType' object has no attribute 'create_ytdl_player'

该机器人通常在我自己的PC上运行，但是我当前在Heroku服务器上运行。该漫游器加入了频道，但不播放音频。

我不知道如何解决这个问题 预先感谢您的帮助。