This message remains in the specification only for reasons of backward compatibility with HL7 v 2.1It is used as part of the protocol which creates a generic form of an asynchronous application level acknowledgment, the MCF message. See Section 2.12.1.2, "Response."
The first MCF message, sent after the initial receipt has the following structure.
MCF Delayed Acknowledgment Chapter
MSH Message Header 2
MSA Message Acknowledgment 2
[ ERR ] Error 2
The second MCF message, sent after application processing, has this structure:
MCF Delayed Acknowledgment Chapter
MSH Message Header 2
MSA Message Acknowledgment 2
[ ERR ] Error 2