I owe back child support, can I still get all of the Child Tax Credit?

Probably not.

If you owe back child support, some payments you get from the government can be taken (or "garnished") to pay your child support debt. IRS payments like tax refunds are subject to this process.

Notably, the CTC monthly payments issued in 2021 were not taken to cover child support debts. Any amount you claim this year, though—whether it is the second half of the credit, or the whole credit—can be taken.