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M56 Remark Code: Payer Identifier Missing or Invalid

M56 means a payer identifier on the claim is missing, incomplete, or invalid. It often concerns the identifier for another payer, such as a secondary or supplemental plan, so the claim could not be routed or coordinated.

Quick facts

Code
M56 (RARC M56)
Status
Active In use since January 1, 1997; last modified February 28, 2003.
Code set
Remittance Advice Remark Codes (RARC)
Group codes
  • CO (Contractual Obligation): The claim or crossover cannot be completed until the payer ID is corrected. It is not a patient liability.
Official description
Missing/incomplete/invalid payer identifier.
X12 Remittance Advice Remark Codes, retrieved September 25, 2026
Last verified
against the official X12 list.

What M56 means

Electronic claims identify payers by payer ID. The ID routes the claim to the right destination and, for secondary coverage, lets one payer forward the claim to another. M56 says a payer identifier on the claim was missing, malformed, or did not match any known payer. Depending on which one failed, the claim may be rejected or processed without being forwarded to the other payer.

Common causes

  • The secondary payer ID was left blank on a claim with other insurance.
  • A clearinghouse payer ID was used where the payer’s own identifier was required.
  • The payer changed its ID after a merger or new plan year.
  • A Medigap identifier was entered in the wrong format.
  • Paper claim information in boxes 9 through 9d or 11 was incomplete.

How to fix it

  1. Identify which payer ID failed: primary, secondary, or supplemental.
  2. Look up the current ID from the payer or clearinghouse list.
  3. Correct the claim and resubmit, or bill the other payer directly with the primary remittance.
  4. Update the insurance setup in the patient account.

How to prevent it

Maintain a single, current payer ID table and review it when clearinghouse updates are released. For coordination issues, see eligibility and COB denials.

Codes that may appear with M56

  • CO-16 (Claim/service lacks information or has submission/billing error(s).): The claim lacks information or has billing errors.
  • CO-109 (Claim/service not covered by this payer/contractor.): The claim was sent to a payer that does not cover it.
  • MA92 (Missing plan information for other insurance.): Plan information for other insurance is missing entirely.
  • N245 (Incomplete/invalid plan information for other insurance.): Other insurance plan information is incomplete or invalid.
  • CO-B11 (The claim/service has been transferred to the proper payer/processor for processing.): The claim was transferred to the proper payer for processing.

M56 FAQ

Which payer identifier does M56 refer to?

It can be the destination payer or another payer listed on the claim. On Medicare claims it often concerns the supplemental insurer information needed for crossover.

Where do I find the correct payer ID?

From the payer's provider resources, your clearinghouse's payer list, or the member ID card.

Should I appeal M56?

No. Correct the identifier and resubmit or bill the other payer directly.