The 2 most common reasons this year is you entered the wrong amount on line 30 for the Recovery Rebate Credit (3rd Stimulus payment) or line 28 for the Child Tax Credit. Those lines are just if you didn't already get the full amount or qualify for more. The IRS knows what they already sent you.
Do you have an amount on line 30 or 28? The 3rd Stimulus payment was 1400 per person (2800 married).
They sent the 3rd Stimulus payment starting in March 2021. Double check your bank statements and check your IRS account (both accounts if married) to see what they sent you.
A lot of people answered the questions wrong and tried to claim the credits again. Double check your bank statements to see what the IRS sent you during the year for the 3rd Stimulus payment and Advance Child Tax Credit. And check your IRS account (both accounts if married).
Look at that transcript carefully against the actual 1040 you filed ... it will show the total tax bill and also the "payments" you made thru credits and withholding for a balance due. You may be focused on the total tax bill and not the net. If the IRS did change something on your return you would get a notice in the mail.
1) what is the EXACT amount of the difference between what your expected amount owed and what the transcript says,
2) what is on Line 30 of your tax return (I suspect this is going to be the problem)
2) what is on Line 28 of your tax return.
if you received stimulus money or Advance Child Tax Credit money and didn't report EXACTLY what the IRS sent you when prompted by Turbo Tax, it's going to create an adjustment by the IRS. I'll bet that is the problem.