On June 1, 2023, the IRS issued Tax Tip 2023-75. There, the IRS explained:

When banks, credit unions, businesses and other payers file information returns with data that doesn’t match IRS records, the IRS sends them a CP2100 or CP2100A notice. The notices tell payers that the information returns they submitted have a missing or incorrect Taxpayer Identification Number, name or both.

Each notice has a list of payees with the issues the IRS found. Payers need to compare the accounts on the notice with their account records and correct or update their records, if necessary. Payees may also need to correct their backup withholding on payments made to payees.

The IRS sends CP2100 and CP2100A notices twice a year in September and October and again in April.

Additional Information is found in the tax tip linked above.