Uninsured medical costs

My ex & I are to split uninsured medical costs. Our child was in an accident; insurance was filed, denied because of deductible. An accident insurance that the ex & his wife have was then filed. That insurance has sent them a check for $485 for the accident. There is roughly $1200 in bills associated with the accident. My question: Since that is accident INSURANCE, shouldn’t that money be put towards the bills & then the remainder of the bills be split in half?

I should also add that the ex is NOT required to carry insurance on the kids; they VOLUNTARILY put this coverage on them.

Yes, if you have an agreement to split uncovered medical expenses evenly, it would make sense that the $485 would be considered the covered portion to be applied to the balance, and then the parties split the remainder evenly. Even if not specifically stated in the agreement, that arrangement would seem to be in the spirit of the agreement.