N4 remark code

Remittance advice remark code N4. Remark codes add detail to the reason code on the same claim line.

Prior payer EOB missing or invalid

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 N4 means

The secondary payer needs the primary payer's explanation of benefits and either did not get it or could not use what it got.

A payer processing a claim as secondary or tertiary needs to see how the earlier payer handled it. N4 means that remittance or EOB was not attached, or what came through was incomplete or unreadable.

On electronic claims this often points to missing or mismatched primary payment data in the coordination of benefits loops rather than a missing paper document. It explains a denial reason code and does not stand alone.

Common causes

• The secondary claim went out without the primary payer's paid amounts and adjustments.
• A paper secondary claim was mailed without the primary EOB attached, or with the wrong patient's EOB.
• Primary adjustment amounts on the electronic claim do not balance to the billed charge.
• The attached EOB is illegible or does not show the same dates of service as the claim.

What to do next

1. Pull the primary remittance for the same patient, dates of service and charges.
2. Check that the other payer paid amount, adjustment group codes and reason codes are populated and balance on the claim.
3. Resubmit the secondary claim with the complete primary information or a clean copy of the EOB.
4. Confirm the order of benefits with the patient if the primary payer is in doubt.

Related codes

• N479 (remark code) Other payer EOB missing for COB
• N245 (remark code) Other insurance plan details invalid
• 22 (reason code) Another payer may be primary