Those are generic reasons they give if they changed the Recovery rebate credit on line 30. How much is on 1040 line 30?
Did you receive the full amount for both the first 2 Stimulus payments? Better check your 1040 line 30 and see if an amount is listed. That's been a problem. A common adjustment is if you claimed the Recovery rebate credit on 1040 line 30 when you already got the Stimulus payments or got the second one after you filed. Or you might have answered the Stimulus questions wrong and tried to claim it again or some more on line 30. So the IRS took it off because you already got it. They know they sent it to you.
If you claimed a missing stimulus payment on your return but the IRS took it off you have to ask the IRS. They think they already sent it to you. Maybe it went to an account you don't remember. Or you got a check or a card. It was probably easy to miss the debit card in the mail and think it was junk mail. They have to put a trace on it.
How to put a trace on a missing 1st or 2nd Stimulus payment. IRS for Payment Issued but Lost, Stolen, Destroyed or Not Received
See question F3 here, you can expand it to see how to put a trace on it.
I received a letter from the IRS Letter 6470. I never claimed any dependents and they say I did. They are saying I made over $75,000 and I don’t come near. If I don’t answer the letter they will begin collecting taxes due. There was a problem with RRC payments and I left one accidentally out ( the $600) payment early in the year. I was awaiting the 1040-x or z form from turbo tax to correct and they sent me a letter they had corrected it. Now I get this letter threatening collections and US TAX COURT. I didn’t even make $20,000 as I’m on social security and that’s it. Also, they said I left out the name if one dependent and I never submitted any names whatsoever. I file individually and my grown children (40’s) file their taxes independently. So, I’m clueless what they are doing making up such a scenario.
If you read my answer above those are a list of possible reasons, not the actual reason. The amount you claimed on 1040 line 30 is wrong so they took it off your return. They either reduced your refund or now you owe more.
You seem to know you missed entering a payment you got. So you tried to get it again on line 30. How much was on line 30? You do owe it back. You don't need to amend. Just pay the tax due. There is nothing you can change or fix.