Distinguish 999 functional acknowledgment, TA1 interchange acknowledgment, and 277CA claim acknowledgment and handle each in an EDI pipeline

Verified steps

1. Identify the acknowledgment type by its transaction set ID: TA1 is an interchange-level segment (no ST/SE wrapper) returned when the ISA envelope is malformed; 999 is ST*999 and covers functional group acceptance or rejection; 277CA is ST*277 with a purpose code in BHT indicating acknowledgment of claims receipt
2. For TA1: parse the single TA1 segment fields — TA103 is the interchange control number being acknowledged, TA104 is the acknowledgment code (A=accepted, E=accepted with errors, R=rejected), TA105 is the note code; a rejected TA1 means none of the enclosed transactions were processed and the entire file must be corrected and resubmitted
3. For 999: navigate AK1 (functional group acknowledgment, AK101=transaction set ID), AK2 (transaction set acknowledgment, AK201=control number), IK5 (transaction set response: A accepted, E accepted with errors, R rejected, X rejected — content after decryption); read IK3/IK4 error segments for the specific element position and error code
4. For 277CA: parse CLP segments in Loop 2200D — CLP02 status code '4' indicates the claim was rejected at intake (not clinically adjudicated); STC segments carry category and claim status codes explaining the rejection reason
5. Build a state machine: TA1 rejection triggers file-level resubmit; 999 rejection triggers transaction-level correction; 277CA rejection triggers claim-level correction before resubmission
6. Log control numbers from TA1, AK1/AK2, and TRN segments to correlate each acknowledgment to its original submission for audit