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.
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 .