M56 remark code

Remittance advice remark code M56. Remark codes add detail to the reason code on the same claim line.

Missing or invalid payer identifier

Unofficial reference. This is our own plain-English explanation, not the official code text. Payer rules differ. Verify with the payer and the official X12 code list. AlphaPrefix is not affiliated with X12, CMS or any payer. Data last updated Nov 11, 2026.

What M56 means

The identifier for a payer on the claim, often another payer in coordination of benefits, is missing or not valid.

The payer could not identify a payer named on the claim. This often concerns the other payer information in a secondary or crossover claim, where each payer needs a recognized identifier.

It usually comes with reason code 16. The fix is a corrected claim with the right payer identifier, not an appeal.

Common causes

• The other payer's identifier was entered in the wrong format or left blank.
• An outdated payer ID from an old insurance card or clearinghouse list was used.
• The patient's coverage was set up under the wrong payer in the billing system.

What to do next

1. Confirm the payer's current identifier with the clearinghouse payer list or the payer.
2. Update the insurance setup for the patient in the billing system.
3. Resubmit the corrected claim with the updated payer identifier.

Related codes

• 16 (reason code) Missing information or billing error
• MA04 (remark code) Primary payer information needed
• MA92 (remark code) Other insurance plan details missing