Discord Bot Code Syntax Error - Line 18

Python
#1 
import discord
import os 

client = discord.Client()

@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.startswith('$hello'):
    await message.channel.send('Hello!'')

client.run(os.getenv('TOKEN'))

This is my code. I was trying to follow the tutorial on making a Discord Bot but for some reason, it keeps giving me a syntax error for line 18. I am a beginner so I personally don’t know what is wrong.

This is the link to the tutorial I was watching. I was only at 20 minute mark.
FreeCodeCamp’s Discord Bot Tutorial

#2

you have two quotes when you should have only one, meaning you have a non closed string, everything after that is considered a string