Ex-wife said son made too much money to be my dependent (I claim per divorce decree). He's 19, student for half of 2020. I pay support on him. Is he still my dependent?

The ex-wife's tax preparer said that he made too much money to be a dependent, even though he is a student (lives at home). He filed taxes on his own (like he usually does), but the tax preparer did not state that "someone else claiming him as a dependent".  Per the divorce decree, I claim him as a dependent.  Who is in the wrong?  Me claiming him as a dependent or the tax preparer?