The taxpayer’s 9 digit Social Security number should be written on the front side of the check as such:“SSN #” and then the 9 digits.
The form and year that the check is for should also be written on the front side of the check. For example, if the payment is for 2022 for Form 1040-ES, then “2022 Form 1040-ES” must be written on the check.
The check should be mailed to:
Internal Revenue Service P.O. Box 1300 Charlotte, NC 28201-1300 USA