I made a discord bot, but it is not responding at all. The bot is hosted on repl.it.

My Code:

```
import discord
import os

client = discord.Client()

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

async def on_message(message):
    if message.author == client.user:
        return

    if message.content.startswith('$buy'):
       await message.channel.send('What would you like to buy' + message.author)
client.run(os.getenv('TOKEN'))

```

Thanks in advance