After you file

On the Form 1040 Line 24 is a calculated number based on Lines 16 thru 23.  Which of those Line numbers is the IRS indicating as incorrect?

The tax on the taxable income on Line 16?

Child Tax Credits from Schedule 8812?

The amount from Schedule 2 Line 3?

The amount from Schedule 3 Line 8?

Other taxes, including self-employment taxes from Schedule 2 Line 21?

 

https://www.irs.gov/pub/irs-pdf/f1040.pdf