Standards & EDI
999 (Implementation Acknowledgment)
Draft — pending verification
This reference entry has not yet been verified against its authoritative source (Original definitions; regulatory facts to be verified against CMS-0057-F (89 FR 8758) and X12/HL7 documentation). Do not rely on it for production configuration until this notice is removed.
In more depth
A rejected 999 means the request never reached adjudication, which matters for turnaround-time analysis: the clock and the provider's expectations start at submission, so silent 999 rejections that no one monitors become mystery delays. Real-time 278 flows surface these problems as immediate errors instead.