The payer is telling you something is missing from the claim itself. CO-16 almost always arrives with a remark code that names the missing piece, so read the full remittance line, not just the CARC.
In chiropractic billing the missing piece is usually a modifier: AT on Medicare CMT lines, 25 on an exam billed with an adjustment, 59 or XS on 97140 performed the same day as CMT, or GP on therapy codes for payers that require it. Missing diagnosis pointers and a missing initial treatment date are the next most common culprits.
A Tuesday visit goes out as 98941 with the AT modifier missing because the fee schedule template dropped it during an update. Medicare pays nothing and the ERA shows CO-16 with a remark code pointing at a missing required modifier. The service was fine, the documentation was fine, and the claim still earned zero because one two letter modifier fell off.
Medicare requires the AT modifier on chiropractic manipulation claims to indicate active treatment; claims without it are treated as maintenance and denied. The requirement lives in the Medicare Claims Processing Manual, Chapter 12.
Cervica reads the CARC and remark codes off the ERA automatically, lands the claim in the denial worklist under Correct and resubmit, and suggests the exact modifier fixes that match the lines on the claim. The claim scrubber also catches most of these before the claim ever goes out.
General information for billing teams, not legal or payer specific advice. CARC definitions belong to X12; payer policies vary and control. Verify against the payer contract before acting on any individual claim.