Discordのbotをpythonで作っていたのですが下のコマンドが使えません。なぜでしょうか？

import random
import discord 

@client.event
async def on_ready():
    print('We have logged in as {0.user}'.format(client))

@client.event
async def on_message(message):
    if message.content == "$dice":
        mylist = ["1", "2", "3", "4", "5", "6"]
        await message.send_message(random.choice(mylist))

client.run('token')