If the tp claims a child in 2020 that was claimed by their ex-wife in 2019, does the tp deserve the stimulus amounts for the child?

In this case, the tp entered the correct amounts of EIP he received, but then the IRS disallowed the credit because he hadn't claimed the child in 2019. If we protest this because he actually claimed the child in 2020, who would the IRS side with? Has anyone else dealt with this situation?

- Ky