Pacun,
I had a similar scenario. Client made an estimated payment for 20k to be applied to the 2022 tax year in Feb 2023. The filing time was extended due to NC being claimed a disaster area due to Hurricane Ian. The IRS did not provide a means to properly route the estimated payment to the proper year becasue of the filing extension. Calling the PPL, first agent said no problem and supposedly put in motion to move the funds from 2023 to 2022. Called back 3 weeks later and was told that the PPL agents did not have authority to move the funds and that everything I was told was not true. Good thing I recorded names and agent ID's The agent went to their supervisor and after they realized this was their mistake, made an exception and correctly moved the funds. Because your client made the error, they may be less than cooperative. Be ready to apply for a refund for the overpayment for the wrong year that was used. Personally, I would require payment to help this client. It is not your error, they can pursue it themselves or pay you to do it with no guarantees. I would tell the client to get his mess straightened up, pay what is owed and then work to get the overpayment, if any, back. They may have already applied the overpayment to what he owes. If that is the case, then tell him to pay the balance and move on.