MLLP.ClientContract.send

You're seeing just the callback send, go back to MLLP.ClientContract module for more information.
Link to this callback

send( pid, payload, options, timeout )

Specs

send(
  pid :: pid(),
  payload :: HL7.Message.t() | String.t(),
  options :: send_options(),
  timeout :: non_neg_integer()
) ::
  {:ok, String.t()}
  | MLLP.Ack.ack_verification_result()
  | {:error, client_error()}