N823 remark code

Remittance advice remark code N823. Remark codes add detail to the reason code on the same claim line.

Procedure modifier invalid or incomplete

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 N823 means

A modifier on the line is not valid, does not fit the procedure code, or is incomplete, so the line cannot be processed as billed.

N823 says the payer read the modifier on the line and could not accept it. The modifier may not exist or have expired, may not be allowed with that procedure code or claim type, or may be one the payer does not recognize.

It is a remark code, so it explains a claim adjustment reason code on the same line rather than standing on its own. It is usually paired with reason code 4 (modifier does not fit the code) or 16 (missing information or billing error). The usual fix is a corrected claim with the right modifier, not an appeal.

Common causes

• The modifier is not allowed with that procedure code, such as a component modifier on a code with no separate components.
• A modifier was entered in the wrong format, such as a typo, an extra character or the letter O instead of zero.
• A modifier the payer does not accept was used, such as a payer specific or telehealth modifier from another payer's rules.
• The modifier conflicts with the place of service, the provider type or another modifier on the line.
• A retired modifier was used for a date of service after it stopped being valid.

What to do next

1. Look at the exact modifiers on the denied line and check each one against the procedure code and the date of service.
2. Check the payer's modifier policy, since accepted modifiers and pairings vary by payer.
3. Confirm with the coder that the documentation supports the modifier you choose.
4. Send a corrected claim with the right modifier, or with the invalid one removed.
5. Fix the charge or template that added the wrong modifier so future claims go out clean.

Related codes

• 4 (reason code) Procedure code and modifier do not match
• 16 (reason code) Missing information or billing error
• N822 (remark code) Procedure modifier missing
• N519 (remark code) Invalid modifier combination