Hello old friends

Order says we split out of pocket medical expenses 50/50.
Custodial Ex finally used the new insurance and I got the notification from BCBS that he took YDS to the doctor and so much was paid for this and that and $72 would be owed to the provider. It's not a bill, just a notification that a bill is coming.
Now, it's one thing if ex asks me to pay my half but I doubt custodial ex will pay it at all. I'm confident he'll ignore it like any other non-utility bill. But am I ultimately responsible for it since I'm the insured? I don't think I'm the guarantor at the pediatrician since i had that changed years ago.
