@johntheretiree use any option you want to pay what you owe. The IRS is not going to turn down money!
if you fed-x, then include the form 1040V and write "2024 tax year" on the check. They will post it to 2024 and all will be good. And if you just send the check with no voucher, on the memo line of the check simply write your social security number and the words "2024 tax year" and it will get posted properly. And if it doesn't, you have proof from the cancelled check what you CLEAR intent was.
