A maximum cahout level means that's the maximum amount you can withdraw from the bonus.
It doesn't mean that if you go over that amount you won't be able to cashout.
For example, say you are given a $50 free bonus with a maximum cashout of $100. You reach the playthrough and hit a big win and have a balance of $333. You would be eligible to cashout $100 of that $333 and they would remove the additional $233 from your account.