If you pay online you get an immediate confirmation number. Nothing "lost in the mail" of unopened correspondence by the IRS.
IRS E-News 2021-33
"The IRS is closing several individual payment P.O. boxes (or lockbox addresses) in the San Francisco, Calif., and Hartford, Conn., areas beginning Jan. 1, 2022. Payments mailed to these closed payment locations after Jan. 1 will be returned to sender. To help ensure timely receipt, encourage your clients to avoid mailing to these closing addresses. Check Where to File on IRS.gov for active addresses before mailing payments. If you or your client receive an IRS payment letter, send payment to the address found in the letter. The IRS also encourages taxpayers to use IRS Direct Pay. It’s a fast, secure and easy way to pay a tax bill or estimated tax payment directly from a checking or savings account. Users receive instant confirmation that their payment has been made. For more information, see Publication 3891, Lockbox Addresses for 2021."