Can I claim my son as a dependent, even though he lived with his dad for all of 2019, because my ex can't claim him because he is behind in his child support payments?

[skj081068]

what happens if an ex-spouse is behind on his child support payments?

[Anonymous]

you ex can grant you permission to claim you son by providing you with form 8332. 

Note: If you are filing your return
electronically, you must file Form 8332 with
Form 8453, U.S. Individual Income Tax
Transmittal for an IRS e-file Return. See Form
8453 and its instructions for more details.

being behind in child support has nothing to do with federal rules for claiming a dependent. 

maybe there's something in your divorce decree but the IRS doesn't care.