That is my thought, if your not claiming the child and receiving the CTC then no mechanism for reconciling the amount of ACTC. 

Excerpt from the FAQ's:

Q L3. My child's other parent received the advance Child Tax Credit payments even though I will be claiming the Child
Tax Credit for our child on my 2021 tax return. Will I still be able to claim the full Child Tax Credit? (updated January
11, 2022)
A3. Yes. You will be able to claim the full amount of the Child Tax Credit for your child on your 2021 tax return even if
the other parent is received advance Child Tax Credit payments. The other parent should have unenrolled from receiving
advance payments, but their decision will not affect your ability to claim the Child Tax Credit.