Is it for the 3rd Stimulus payment or the Child Tax Credit? What letter number is it? Does it list like 5 reasons? Those are just generic reasons. That sounds like the Recovery Rebate Credit on line 30. How much is missing?
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.
The Advance Child Tax Credit payments should have been $300 per month (July-Dec) for each child under the age of 6 plus $250 per month for each child age 6-17 (based on the children listed on your 2020 tax return, but using their ages as of 12/31/21).
A lot of people answered the questions wrong and tried to claim the credits again. Double check your bank statements and Check your IRS account (both accounts if married)
Your Online Account | Internal Revenue Service
