MLLP.ClientContract.send_async

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

send_async( pid, payload, timeout )

Specs

send_async(
  pid :: pid(),
  payload :: HL7.Message.t() | String.t(),
  timeout :: non_neg_integer()
) :: {:ok, :sent} | {:error, client_error()}