What causes a TIN mismatch?

Common causes: transposed digits, legal name on the W-9 does not match IRS records, vendor provided a DBA instead of legal name, LLC changed structure without updating the W-9, or an old EIN was used after a merger. IRS matching compares TIN to the name combination on file with the IRS.

Should we file a 1099 with a known mismatch?

No. Filing with a combination the IRS has flagged produces B-notices and may trigger penalties. Request a corrected W-9 first. If the vendor does not respond within IRS timeframes, follow backup withholding and B-notice procedures.

How do we send a B-notice to a vendor?

Use IRS Form 2106 or 2106-A (or equivalent notice meeting IRS requirements) to solicit corrected TIN information. Send within the timeframe specified in your CP2100 notice. Retain proof of mailing and the vendor's response or non-response.

Can TIN matching prevent mismatches before filing?

Yes. Run IRS TIN matching on your vendor file before 1099 filing season. Proactive matching catches errors weeks before the filing deadline — when you still have time to collect corrected W-9s without emergency escalation.

Guide

How to Fix a TIN Mismatch on a W-9

By Keelstar Team · Updated July 11, 2026

The short answer

When a W-9 TIN fails IRS matching or you receive a CP2100 notice, stop using the bad combination for 1099 filing. Contact the vendor immediately, request a corrected W-9 with the legal name and TIN exactly as IRS records show them, and send a B-notice if required under IRS procedures. Validate the corrected form before filing or making additional reportable payments. Document every outreach attempt, the date you received the correction, and whether backup withholding began. A fixed W-9 today prevents corrected 1099 filings and penalty exposure tomorrow.

How you discover a mismatch

TIN mismatches surface in three ways: your pre-filing TIN matching run flags a bad combination, the IRS sends a CP2100 or CP2100A notice listing proposed mismatches from prior filings, or your intake validation catches an obvious format or name inconsistency on a new W-9. Each path requires the same response — do not ignore or defer.

Immediate steps when a mismatch is flagged

Mark the vendor record as 'TIN mismatch — do not file.' Pull the W-9 on file and compare line 1 name and Part I TIN against what the vendor's invoices and contracts show. Contact the vendor with specific instructions: provide a corrected W-9 with the exact legal name and TIN registered with the IRS.

Stop 1099 filing for that vendor until corrected
Review payment history for reportable amounts
Send secure W-9 re-request with mismatch explanation
Log date discovered and all outreach

Vendor outreach that gets corrections

Generic emails ('please resend your W-9') get ignored. Tell the vendor their name/TIN combination failed IRS matching, specify whether the issue is likely the name, the number, or both, and link to a secure submission portal. Give a deadline — ten business days is common — and note that unresolved mismatches may trigger backup withholding on future payments.

B-notice obligations after CP2100

When the IRS notifies you of mismatches from prior-year filings, you must send affected payees a B-notice soliciting corrected information within the required window. If the payee does not respond with a corrected W-9 within the specified period, begin backup withholding on future reportable payments and document the start date. Coordinate with tax leadership — B-notice timing is statutory.

Validate and update systems

When the corrected W-9 arrives, re-run TIN matching before accepting. Update the vendor master with the new legal name, TIN, and classification. If you already filed a 1099 with the bad combination, prepare a corrected 1099 (Form 1099 correction process). Retain both the original and corrected W-9 with timestamps.

Prevent repeat mismatches

Root-cause analysis matters. If mismatches cluster around LLC vendors, sole proprietors using DBAs, or vendors onboarded without validation, fix the intake process — not just the individual vendor. Run TIN matching at W-9 receipt for high-volume payees and always before bulk 1099 filing.

Frequently asked questions

What causes a TIN mismatch?: Common causes: transposed digits, legal name on the W-9 does not match IRS records, vendor provided a DBA instead of legal name, LLC changed structure without updating the W-9, or an old EIN was used after a merger. IRS matching compares TIN to the name combination on file with the IRS.
Should we file a 1099 with a known mismatch?: No. Filing with a combination the IRS has flagged produces B-notices and may trigger penalties. Request a corrected W-9 first. If the vendor does not respond within IRS timeframes, follow backup withholding and B-notice procedures.
How do we send a B-notice to a vendor?: Use IRS Form 2106 or 2106-A (or equivalent notice meeting IRS requirements) to solicit corrected TIN information. Send within the timeframe specified in your CP2100 notice. Retain proof of mailing and the vendor's response or non-response.
Can TIN matching prevent mismatches before filing?: Yes. Run IRS TIN matching on your vendor file before 1099 filing season. Proactive matching catches errors weeks before the filing deadline — when you still have time to collect corrected W-9s without emergency escalation.

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