What it checks
| Check | What it catches | Fix |
|---|---|---|
| Missing TIN | Blank or placeholder values (000000000, 999999999, "N/A", "APPLIED FOR") | Solicit a W-9; withhold 24% until received |
| Not nine digits | Eight digits (a leading zero stripped by Excel), ten digits, letters | Restore the leading zero from the source document; re-key |
| Invalid SSN structure | Area 000, 666 or 900–999; group 00; serial 0000 | Cannot be a valid SSN; check whether it's an EIN or a typo |
| Never-issued EIN prefix | Two-digit prefixes the IRS has never assigned | Typo, or the number is an SSN entered in EIN format |
| Business name with SSN format | Names containing LLC, Inc, Corp, Co., Ltd, LP, PLLC, PC, Trust with a ###-##-#### number | Likely a disregarded LLC or sole proprietor: line 1 should be the owner's name |
| Duplicate TIN, different names | The same nine digits on two or more vendor records | Merge duplicates; if the names are unrelated, one of them is wrong |
| Same name, different TINs | One vendor name with two numbers | Usually an SSN and an EIN for the same person; keep the pair that matches |
| Sequential or repeated digits | 123456789, 111111111 and the like | Placeholder data; solicit the real TIN |
A file that passes every check can still mismatch at the IRS, because the checks here are about structure and the IRS match is about whether the name and number belong together. That step is what IRS TIN matching does.