If you are not claiming your child---is he listed on your tax return? Are you and the other parent all living together as a family? If so, only one of you should have anything entered on a tax return for the child. Or do you live apart and take turns in some way for who claims the child? Who does the child live with?
A common error is when unmarried parents live together, If you and the other parent live together, only one of you can claim the child for any tax benefit. The TurboTax interview is confusing (it's designed for divorced parents, who are allowed to split the child). The second parent should not enter the child, at all.
If you and the other parent live together, either one of you (but not both) may claim the child. You may decide between you which one will claim the child. Only if you can’t agree, do the IRS tie breaker rules apply, to see who has first choice. It may be worthwhile to prepare trial returns, both ways, to see which way the family comes out best. This tool may be useful: https://turbotax.intuit.com/tax-tools/calculators/taxcaster/?s=1.
I have my son more than his father does. That's how it is listed in our divorce agreement. We agreed that he would claim him on tax returns this time and he did. So I'm not sure why I am being rejected because I'm not trying to claim him.
What is the reject message and reject code?
If you are the custodial parent where the child physically lived for more than half the year (183 nights) then:
When you enter the dependent, you say that he/she is "Your child" (not you and your spouse if remarried),
he/she lived with you the whole year,
“no” the child did not pay more than half of his/her own support,
"yes", you have a custody agreement,
and "yes", the other parent is claiming this year.
That will give you the EIC, Child Care Credit and Head of Household filing status if you otherwise qualify.
The child would be listed as "non-dependent EIC & Dependent Care only".
The other (non-custodial) parent can claim the child’s exemption and child tax credit only and needs a signed 8332 form to do so.