So the general lot of you posting in here probably didn't read OP's post properly, or just don't understand.
1. Missouri Belle is a fictional casino, a subplot in the newly-released season 3 of the fictional TV series Ozark.
2. OP is asking if it's legally OK to use the name of a fictional casino.
I don't know, but I suspect all you need to do is to check if the name is trademarked. Otherwise, I don't see how anyone could sue you for using a name of a place that doesn't even exist. It'll be like making a Slytherin school.
But OP intends to use the name of that fictional casino to generate profits
(well he will build a site so definitely he wants to make money with it) therefore expect that it will be taken down soon, for let's say OP got successfully make it popular and well-established. If just for fun, then he can proceed without worrying.
If OP really wants to follow the name, he can modify it a bit but still close to the name of Missouri Belle. It's the most used method by some business owners to somehow attract their customers. For example, Clash of Burgers derived from Clash of Clans, Foodever 21 derived from Forever 21, etc. - something like that.
