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
This is the same issue I'm having. Turbo Tax will calculate correctly the amount my wife and I have received based on our 2020 incomes. However, it is NOT including the $500 and $600 for my child born in 2019, who was not on our 2020 taxes. So we're $1,100 short.
Why is your child not on your 2020 return? The Recovery rebate credit is only based on 2020 now. You can't get it on 2019 anymore.
Sorry if you do not qualify for the Recovery Rebate Credit because your child is not on 2020 then you will not be able to get the missed stimulus payment.