Nostrum.Voice.connect_to_gateway

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

connect_to_gateway(guild_id)

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Specs

connect_to_gateway(Nostrum.Struct.Guild.id()) :: :ok | {:error, String.t()}

Low-level. Manually connect to voice websockets gateway.

This function should only be called if config option :voice_auto_connect is set to false. By default Nostrum will automatically create a voice gateway when joining a channel.