One request's outcome in a batch: the custom_id it was submitted with and the result it ended in.

Match on result to handle each outcome:

case result do
  %BatchResult{custom_id: id, result: {:ok, message}} -> store(id, message)
  %BatchResult{result: {:error, error}} -> log(error)
  %BatchResult{result: :canceled} -> :ok
  %BatchResult{result: :expired} -> requeue(result.custom_id)
end

Expired requests aren't billed — those are ones the batch's 24 hours ran out on before they reached the model.