Make sure your child is showing up as a dependent. Do you have a high 2020 income? Did you enter just the actual amounts you got in the 2 boxes? You don't have an amount on 1040 line 30?
Do you have any other children? Like maybe one that turned 17?
The Recovery rebate credit is really based on your 2020 income and situation. If you do not qualify for the Recovery Rebate Credit because of your 2020 tax situation then you will not be able to get the missed stimulus payment.
