Nostrum.Voice.leave_channel

You're seeing just the function leave_channel, go back to Nostrum.Voice module for more information.

leave_channel(guild_id)

leave_channel(Nostrum.Struct.Guild.id()) :: no_return() | :ok

Leaves the voice channel of the given guild id.

This function is equivalent to calling Nostrum.Api.update_voice_state(guild_id, nil).