Mom and Dad had 2 children together but never married. Lived together until 3 years ago (children are 9 and 8). Since the split Mom has always put 1 of the 2 children on her income tax return.Dad puts the other child on his return. For 2021 Dad decides to do his own tax return thru Turbo Tax and puts both children on his return and files head of household (children live with Mom and Dad takes the kids on the weekend). Now that both children are on the Dad's return it is rejecting Mom as she still took the same dependent (which Dad has now put on his return). Dad said child was on the return but he didn't take any of the credits (EIP or CTC). Wrong - Dad got the EIP pmt for the child that is now on Dad's return that Mom normally has on her return. Now Mom cannot file (as her tax return rejected) unless she takes the child off her return. When I wrote this question I thought Dad had just put the second child on his return, but didn't take any credits. He clearly didn't take the CTC as its not marked or calculated on the return but he did get the $1400 recovery payment. Originally, I was thinking that he could just take the child off (since he said he didn't take any of the credits), but this did not turn out to be the case. Dad also claimed HOH and the children live with the MOM full time. As for the Tie Breaker rules Mom would get both children if they can't decide who is claimed on both returns.

Therefore, my original question was if Dad put Mom's dependent on his return, but answered the questions so he didn't get any of the credits or recovery credits and then Mom puts the same dependent on her return but takes the credits would Mom's return still be rejected because the child is still listed on both returns?