My cog Command won't work

So I recently added cogs to my discord bot, and for some reason, it won't send the command when I message it and it won't send an error, I'd like to know if you could help me out if I'm doing something wrong.

Code:
@commands.command()
async def avatar(ctx, member: nextcord.Member=None):
if member is None:
member = ctx.author

favatar = nextcord.Embed(title=f"{member.name}'s avatar", color=member.color)
favatar.set_footer(text=f"Requested by {ctx.author.name}#{ctx.author.discriminator}")
favatar.set_image(url='{}'.format(member.avatar_url))

await ctx.send(embed = favatar)

also would like to know if cogs are even worth it, and if so, why?

Voters