M77 remark code

Remittance advice remark code M77. Remark codes add detail to the reason code on the same claim line.

Missing or wrong place of service

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 M77 means

The place of service code is missing, not valid, or does not fit the service billed.

The place of service tells the payer where the patient was when the service was given, which affects coverage and pricing. This remark says the code was missing, invalid, or did not make sense with the service or provider type.

It usually comes with reason code 5, 16 or 58. It often shows up after a telehealth or facility billing change.

Common causes

• The place of service code was left blank or entered in the wrong format.
• The code chosen does not match where the service actually happened, such as office versus hospital outpatient.
• The service is not allowed in the place of service billed.

What to do next

1. Confirm where the patient actually was at the time of the service.
2. Check the payer's rules for which place of service codes apply to the service.
3. Send a corrected claim with the right place of service.

Related codes

• 16 (reason code) Missing information or billing error
• MA114 (remark code) Missing or invalid service location
• M2 (remark code) Patient was an inpatient at the time