Discord.pyで絵文字名（:○○:）からリアクションをつける方法がわからない

前提・実現したいこと

Discord.pyで、投票機能を作っています。
リアクションを追加しようとした時に以下のエラーメッセージが発生しました。

発生している問題・エラーメッセージ

Ignoring exception in on_command_error
Traceback (most recent call last):
  File "C:\develop\python\lib\site-packages\discord\ext\commands\core.py", line 83, in wrapped
    ret = await coro(*args, **kwargs)
  File "main.py", line 690, in vote
    await m.add_reaction(f":{Numbers[sfi]}:")
  File "C:\develop\python\lib\site-packages\discord\message.py", line 928, in add_reaction
    await self._state.http.add_reaction(self.channel.id, self.id, emoji)
  File "C:\develop\python\lib\site-packages\discord\http.py", line 225, in request
    raise HTTPException(r, data)
discord.errors.HTTPException: 400 Bad Request (error code: 10014): Unknown Emoji

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "C:\develop\python\lib\site-packages\discord\client.py", line 312, in _run_event
    await coro(*args, **kwargs)
  File "main.py", line 601, in on_command_error
    raise error
  File "C:\develop\python\lib\site-packages\discord\ext\commands\bot.py", line 892, in invoke
    await ctx.command.invoke(ctx)
  File "C:\develop\python\lib\site-packages\discord\ext\commands\core.py", line 797, in invoke
    await injected(*ctx.args, **ctx.kwargs)
  File "C:\develop\python\lib\site-packages\discord\ext\commands\core.py", line 92, in wrapped
    raise CommandInvokeError(exc) from exc
discord.ext.commands.errors.CommandInvokeError: Command raised an exception: HTTPException: 400 Bad Request (error code: 10014): Unknown Emoji

該当のソースコード

python
1Numbers=["one","two","three","four","five","six","seven","eight","nine","keycap_ten"]
2#------中略------
3@bot.command()
4async def vote(ctx,title,time: int,*select):
5	if len(select) > 10:
6		e=discord.Embed(title="選択肢が多すぎます。",description="選択肢は10個以下にして下さい。",color=Error)
7		await ctx.send(embed=e)
8		return
9#------中略------
10	m=await ctx.send(embed=e)
11	for sfi in range(len(select)):
12		print(Numbers[sfi])
13		await m.add_reaction(f":{Numbers[sfi]}:")