M77 Remark Code: Missing or Invalid Place of Service
Remark code M77 means the place of service (POS) information on the claim is missing, incomplete, invalid, or inappropriate - the two-digit POS code either is not there, is not a real code, or conflicts with the service billed. Like the other M-series remark codes it usually accompanies CO-16, pointing you at the exact field to fix.
Common Causes
- The POS code missing from the claim or entered as an invalid value
- A POS that conflicts with the procedure (a facility-only procedure billed with an office POS, or vice versa)
- Telehealth services billed with the wrong POS for the payer's current telehealth rules (POS 02 vs 10 vs the in-person location, plus modifier expectations)
- The POS not matching the payer's records for where that provider practices
- Facility fees and professional claims disagreeing about where the service happened
How to Fix M77
- Confirm where the service actually occurred and select the matching POS code from the current POS code set
- Check the procedure's setting restrictions - some codes are payable only in specific settings
- For telehealth, apply the payer's current POS and modifier rules (they differ between Medicare and commercial payers and have changed repeatedly)
- Align the professional claim's POS with the facility claim when both exist
- Correct the POS and resubmit; M77 is a data fix, not an appeal
Frequently Asked Questions
M77 means the place of service on the claim is missing, invalid, or inappropriate for the service billed. It arrives with CO-16 and is resolved by correcting the two-digit POS code and resubmitting.
Telehealth POS rules are payer-specific and have shifted often: some payers want POS 02 or 10 with no modifier, others want the in-person POS with modifier 95. Billing one payer's convention to another commonly triggers place-of-service edits like M77.
Related Denial Codes
Related Resources
Claim adjustment reason codes and remittance advice remark codes are standardized code sets maintained by X12. The explanations on this page are written in our own words for educational purposes, based on public CMS and Medicare contractor documentation. Payer policies vary - always confirm handling with the specific payer's guidance and your contracts.