Python Discord Bot is online, but not work

My Code runs successfully, and it turns to be online. but bot doesn't response to me in text channel. I don't know what's the problem. Plz help.

import discord

client = discord.Client(intents=discord.Intents.default())

@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.author == client.user: 
        return

    if message.content == "$hello": 
        await message.channel.send('Hello!')

client.run("MTAyMjM2NTgwMDU1Nzk4MTcxNw.G4F7Kn.HQHn-MYBUNbz-xJFRJ00KfnHgRuKmxVEFTe1_Q")

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