After you file

That sounds like the list of generic reasons they give if they changed the Recovery rebate credit on line 30.  How much is on 1040 line 30?

 

A common adjustment is if you claimed the Recovery rebate credit on 1040 line 30 when you already got the Stimulus payment or got the second one after you filed or reported the wrong amounts or entered the wrong amounts in the 2 boxes.  If you entered the total you got for both rounds in the same box it would think you didn't get the other one.  The IRS knows how much they already sent you.  You might have tried to claim it again on line 30.