CO-15
Often appealableAuthorization number missing or invalid
Group CO — Contractual Obligation — an adjustment tied to the contract between the insurer and the provider. You usually cannot be billed for a CO amount.
CO-15 means an authorization was required and the authorization number on the claim is missing, invalid, or doesn't match the service billed. It's closely related to CO-197 but focuses on the authorization number itself rather than whether authorization existed.
It's a Contractual Obligation (CO). Frequently the authorization exists but the number was entered incorrectly or didn't match the final codes, which the provider can correct.
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Why you're seeing CO-15
- The authorization number was left off or entered incorrectly.
- The authorization was for a different service or code than what was billed.
- The authorization had expired by the date of service.
Can you appeal it?
Frequently a quick fix when a valid authorization exists — the provider supplies or corrects the number and resubmits.
What to do next
- 1Confirm with the provider whether a valid authorization exists for this service.
- 2If it does, have them add or correct the authorization number and resubmit.
- 3If no authorization was obtained, follow the CO-197 path and request retroactive authorization.
Evidence that helps
- The authorization approval showing the number and covered services.
- The referral or order tied to the authorization.
Frequently asked questions
How is CO-15 different from CO-197?
CO-197 means authorization was required and none is on file. CO-15 means an authorization number is present but missing, invalid, or doesn't match the service. CO-15 is often just a data fix when a valid authorization actually exists.
Related guide: How to appeal a “Prior authorization issue” denial →
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Other common denial codes
Last reviewed July 18, 2026. Denial-code lists (CARC/RARC) are updated three times a year; we review these explanations against the current list.
Sources & references
These explanations are written in plain language and based on the authoritative sources below. Always confirm the specifics against your own plan documents and denial letter.
- ASC X12 — Claim Adjustment Reason Codes (CARC)
The standards body that maintains the official CARC list (the CO/PR codes), updated three times a year.
- CMS / X12 — Remittance Advice Remark Codes (RARC)
The remark codes (N-/M- codes) that accompany a CARC and give the specific reason for an adjustment.
- HealthCare.gov — Appealing a health plan decision
Official overview of internal appeals and external review rights for Marketplace and most private plans.
- U.S. Department of Labor — ERISA claims & appeals
Governs claim and appeal procedures and deadlines for most employer-sponsored (ERISA) health plans.
- Your state's insurance regulator
State agencies enforce external review and consumer protections; find yours via the NAIC directory.
Important: this is not legal or medical advice.
AppealBrain is a free, self-help tool that helps you draft an appeal letter using the information you provide. We are not a law firm, medical provider, or insurance company, and using this tool does not create an attorney–client relationship. Appeal rules and deadlines vary by plan and state — always review your own denial letter and plan documents, and consider consulting a licensed professional for your specific situation. We do not guarantee any outcome.