Did you have 1,000 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.
