AMQPHelpers.Adapter.nack

You're seeing just the callback nack, go back to AMQPHelpers.Adapter module for more information.

nack(channel, delivery_tag, options)

nack(
  channel :: AMQP.Channel.t(),
  delivery_tag :: integer(),
  options :: keyword()
) :: :ok | {:error, term()}

Negative acknowledges of one or more messages.