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N55 Remark Code: Provider Billing Rules Not Followed

N55 means the payer's procedures for billing with group, referring, or performing providers were not followed. The provider information on the claim, such as which NPI appears as billing, rendering, or referring, was not reported the way the payer requires.

Quick facts

Code
N55 (RARC N55)
Status
Active In use since January 1, 2000.
Code set
Remittance Advice Remark Codes (RARC)
Group codes
  • CO (Contractual Obligation): The error is on the provider side and the amount is not billable to the patient while it can be corrected.
  • PI (Payer Initiated Reduction): Some government payers use a payer-initiated adjustment for the same reporting error.
Official description
Procedures for billing with group/referring/performing providers were not followed.
X12 Remittance Advice Remark Codes, retrieved September 25, 2026
Last verified
against the official X12 list.

What N55 means

Professional claims can list several providers: the billing provider (often a group), the rendering provider who performed the service, and sometimes a referring, ordering, or supervising provider. Each payer has rules on how these must be reported and how they must relate to each other in its enrollment records. N55 says the claim did not follow those rules.

It typically explains CARC 16, and can also accompany CARC 185 or CARC 183 when the payer views a listed provider as ineligible in that role.

Common causes

  • The group NPI was placed in the rendering provider field (box 24J) instead of the individual’s NPI.
  • The rendering provider is not linked to the billing group in the payer’s enrollment.
  • A referring provider was required but omitted from box 17 and 17b.
  • A supervising provider was reported where the payer expected the rendering provider, or vice versa.
  • A mid-level practitioner’s services were billed under a physician without meeting the payer’s supervision or incident-to rules.

How to fix it

  1. Read the payer’s provider reporting rules for claims from groups, facilities, and mid-level practitioners.
  2. Map each role correctly: billing provider in box 33 and 33a, rendering provider in box 24J, referring or ordering provider in box 17 and 17b.
  3. Check enrollment linkage so the rendering provider is affiliated with the billing group for the payer.
  4. Submit a corrected claim with resubmission code 7.

How to prevent it

Keep a payer-by-payer matrix of provider reporting rules and enrollment status. Configure your billing system so each provider’s role is populated automatically, and verify enrollment linkage whenever someone joins or leaves the group. Our enrollment and NPI guide covers common setups.

Codes that may appear with N55

  • CO-16 (Claim/service lacks information or has submission/billing error(s).): A submission or billing error in the provider fields.
  • CO-185 (The rendering provider is not eligible to perform the service billed.): The rendering provider is not eligible to perform the service billed.
  • CO-183 (The referring provider is not eligible to refer the service billed.): The referring provider is not eligible to refer the service billed.
  • N32 (Claim must be submitted by the provider who rendered the service.): The claim must be submitted by the provider who rendered the service.
  • N198 (Rendering provider must be affiliated with the pay-to provider.): The rendering provider must be affiliated with the pay-to provider.
  • N290 (Missing/incomplete/invalid rendering provider primary identifier.): The rendering provider's primary identifier is missing or invalid.
  • N286 (Missing/incomplete/invalid referring provider primary identifier.): The referring provider's primary identifier is missing or invalid.

N55 FAQ

Should the group NPI or individual NPI go in box 24J?

The rendering provider field is for the individual who performed the service. The group's NPI generally goes in the billing provider field (box 33a). Some payers have exceptions, so check their guide.

What if a solo practitioner bills?

A solo provider billing under their own NPI may not need a separate rendering provider entry. Reporting the same NPI in both places can be fine or can cause errors depending on the payer.

How is N55 different from an invalid NPI?

The NPIs may all be valid. N55 is about using them in the wrong places or in a combination the payer's enrollment records do not support.