An Implementation Acknowledgment (999) notifies the sender whether the X12 interchange is successfully received by the receiver. The acknowledgment reports any syntactic errors in the Functional Group Response Header and Functional Group Response Trailer.

The 999 segment in the acknowledgment contains the same functional group response number as specified in the control header of the X12 interchange for which the acknowledgment is prepared.

The 999 does not report the status of the functional groups and transaction sets within the interchange envelope.