Just verify that your entries are correct, as I suggest in my 4/14/2022 post above.
But if you've input everything correctly, your return will continue to reject. You'll need to paper-file your return if you want to claim the credit.
If someone else has used your child's number for the credit on their return, which is apparently what's happened, the IRS won't allow you to electronically file as long as your return claims this child for the credit. It's in their database for the year now.
@Nicole B
