Option #2 means that you figured the correct amount on Form 8812, but transferred it to Form 1040 incorrectly. And that’s extremely unlikely when you’re using a tax program.
You are talking about your tax year 2021 return, correct?
If you can’t figure this out, there should be contact information on the IRS notice. You may or may not be able to get through on the phone lines in a reasonable amount of time, but you should be able to reach out by mail, anyway, to see what the issue was.
You might also check the IRS’ Your Online Account tool. You can double-check to make sure you didn’t receive any advance child tax credit.
