This message is used to indicate whether PKB received your message successfully or not. There is 1 success code (AA) and 2 error codes (AR or AE) that can be returned in MSA-1.1.
AR is used to indicate an error condition that we have checked for, e.g. a mandatory field was not included.
AE is used to indicate an unexpected error occurred.
PKB will respond with an ACK message; there are three possible acknowledgement codes.
AA: Message received successfully
AR: Message rejected due to validation errors (detail included)
AE: Unexpected error during processing (usually due to a severely malformed message)