How did you pay the additional amount? Did you use a form like a 1040ES or 1040V or pay Online? Maybe the IRS applied it to the wrong year or to something else.
Do you get Social Security? Is there an amount on 1040 line 6b or is it 0? If you have a lot of other income then up to 85% of SS can be taxable on line 6b. I would compare 2024 to 2023 tax return and see if you had more taxable Social Security on line 6b last year. Was it missed on 2024?
