Q. Do I put in what he got?
A. No.
As Catina T1 stated, It's a tax loop hole, you both get the money! Be sure the ex doesn't try to claim the child on his 2020 return.
From CatinaT1's reference:
"Parents who are not married to each other and do not file a joint return cannot both claim their qualifying child as a dependent. The parent who claimed their child on their 2019 return may have received an additional Economic Impact Payment for their qualifying child. When the parent who did not receive an additional payment files their 2020 tax return next year, they may be able to claim up to an additional $500 per-child amount on that return if they qualify to claim the child as their qualifying child for 2020."
