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M77 Remark Code: Invalid or Inappropriate Place of Service

M77 means the place of service (POS) code on the claim was missing, incomplete, invalid, or inappropriate for the service. It usually accompanies CO-16 or CO-5 and requires a corrected POS in box 24B before the payer will pay.

Quick facts

Code
M77 (RARC M77)
Status
Active In use since January 1, 1997; last modified March 14, 2014.
Code set
Remittance Advice Remark Codes (RARC)
Group codes
  • CO (Contractual Obligation): The line was not paid due to a POS problem the provider must correct. The patient should not be billed.
Official description
Missing/incomplete/invalid/inappropriate place of service.
X12 Remittance Advice Remark Codes, retrieved September 25, 2026
Last verified
against the official X12 list.

What M77 means

The place of service code is a two-digit value that tells the payer where the patient received care: office, patient’s home, inpatient hospital, outpatient hospital, telehealth, and so on. Payers use it for pricing and to decide whether a service makes sense in that setting. M77 covers four different problems with that code: it is missing, incomplete, invalid (not a real POS value), or inappropriate (valid, but wrong for the service or the patient’s status).

The official text was broadened in 2014 to include “inappropriate,” which is why M77 can appear even when the POS code on your claim looks perfectly formed.

Common causes

  • Default POS in the practice management system left unchanged for services done elsewhere, such as hospital rounds billed with the office code.
  • Telehealth services billed with a POS the payer does not accept for virtual care, or with the in-person code when the payer requires a telehealth code.
  • A patient who was a registered hospital inpatient or outpatient on the date of service, making a non-facility POS inappropriate.
  • A service that cannot logically be performed in the reported setting.

How to fix it

  1. Identify where the patient physically was, and whether they were registered as a hospital or facility patient at the time.
  2. Pick the POS code that matches, following the payer’s telehealth rules where relevant.
  3. Update box 24B (or the electronic equivalent) and check that the facility address in box 32 is consistent.
  4. Resubmit as a corrected claim with frequency code 7 if the original was adjudicated.

How to prevent it

  • Set POS defaults per location and per encounter type instead of one practice-wide value.
  • Cross-check hospital census or facility schedules for patients seen outside the office.
  • Catch POS/service mismatches with a Claims Validator before submission.

See also the CO-16 guide.

Codes that may appear with M77

  • CO-16 (Claim/service lacks information or has submission/billing error(s).): The POS was missing or not a valid value, so the claim lacks required information.
  • CO-5 (The procedure code/type of bill is inconsistent with the place of service.): The procedure code is inconsistent with the place of service reported.
  • CO-58 (Treatment was deemed by the payer to have been rendered in an inappropriate or invalid place of service.): The payer decided the treatment was rendered in an inappropriate or invalid setting.
  • N428 (Not covered when performed in this place of service.): A coverage message that the service is not covered in this setting, rather than a coding error.
  • MA114 (Missing/incomplete/invalid information on where the services were furnished.): About the service facility location information, not the POS code itself.

M77 FAQ

Where does the place of service code go?

On the CMS-1500, in box 24B for each service line. Electronic claims carry it at the claim level, with line-level overrides when needed.

What does 'inappropriate' place of service mean?

The code is valid but does not fit the service or the patient's status, for example an office POS on a service provided while the patient was a hospital inpatient.

Can a wrong POS change my payment even if it is not denied?

Yes. Many fee schedules pay facility and non-facility rates differently, so a wrong POS can lead to over- or underpayment and later recoupment.