In my opinion it's a substantial bug but again I'm not qualified or educated enough on it. But if I can exploit it then others would have fun. Very reputable casino with a large reach. I've contacted support and waiting. No bounty page on their site but for sure reputable so I hope they would compensate given the bug.
If that has been found for the very first time then I think that you will be compensated for it but then, they can always claim that it has been reported before and they are just taking time for their actions to be made and fix that bug you have found. Since it is holidays, very few working force and many probably are on leave to cater that bug. Means that they can void it and say something like that but I just hope that you will get significant bounty for it and good luck.