Getting a Null Error everytime I run my Discord.py Music Bot's play command

Question

I am recently making a Discord music bot, and everything works just fine, but when I connect the music bot to a VC and use my play command, it shows me this error:

[NULL @ 0x55f5c64eb340] Unable to find a suitable output format for 'pipe:' pipe:: Invalid argument

Here's a sneak peek of my code:

@commands.command()
async def play(self, ctx, URL):
    FFMPEG_OPTIONS = {'before_options': '-reconnect 1 - reconnect_streamed 1 - reconnect_delay_max 5', 'options': '-vn'}
    YDL_OPTIONS = {'format': 'bestaudio'}
    vc = ctx.voice_client

    with youtube_dl.YoutubeDL(YDL_OPTIONS) as ydl:
        info = ydl.extract_info(url, download=False)
        url2 = info['formats'][0]['url']
        source = await discord.FFmpegOpusAudio.from_probe(url2, **FFMPEG_OPTIONS)
        vc.play(source)