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CO-124 Denial Code (Deactivated): Refund, Not Our Patient

CO-124 identified a payer refund because the patient turned out not to be the payer's member. X12 deactivated it and refers users to the implementation guide for handling reversals, without naming another code.

X12 deactivated CARC124 on June 30, 2007. Payers should no longer use it on new remittances, but it can still appear on older ERAs, corrected claims, and appeals.

Code: CO-124 (CARC 124)
Status: Deactivated StoppedJune 30, 2007 (in use since January 1, 1995).
Code set: Claim Adjustment Reason Codes (CARC)
Group codes: CO (Contractual Obligation): The recovered payment was the provider's to return; the patient's balance was not affected by the code itself.
Official description: Payer refund amount - not our patient.
X12 Claim Adjustment Reason Codes, retrieved September 25, 2026
Last verified: September 24, 2026 against the official X12 list.

What CO-124 meant

CARC 124 explained a clawback. The payer had paid the claim, then discovered the person treated was not its insured for that service, and the remittance line reflected the refund owed back to the payer. It differs from CO-123 in that the reason for the refund was eligibility, not an ordinary overpayment.

What replaced it

X12 did not name a replacement code and instead points to the implementation guide’s reversal rules. Current remittances typically reverse the original claim, and the reason the patient was not covered appears with active codes such as CO-31 for a patient who cannot be identified as the payer’s insured, CO-140 for an ID and name mismatch, or CO-109 when another payer is responsible.

If you still see CO-124

It will only be in historical data. On any account where a payer took back money for this reason, act quickly: confirm the patient’s identity and insurance, then submit to the correct payer. Some payers allow extra filing time when a claim was paid in error by another plan, but you will need the recovery notice as proof.

CO-31 (Patient cannot be identified as our insured.): Patient cannot be identified as our insured.
CO-140 (Patient/Insured health identification number and name do not match.): Patient or insured health identification number and name do not match.
CO-109 (Claim/service not covered by this payer/contractor.): Claim not covered by this payer; send it to the correct payer.

CO-124 FAQ

Why would a payer pay for someone who is not its member?

Eligibility errors, retroactive terminations, or a mismatched member ID can lead to payment before the payer realizes the person was not covered. The payer then recovers the money.

What do I do after the payer takes the money back?

Find the patient's correct coverage for the date of service and bill that payer, watching its timely filing limit. If there is no other coverage, bill the patient according to your policy.

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