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.
I do hope they hear you out or at least pay you handsomely for the bug. Some brands are so mean when it comes to paying out bug bounties yet if the person inside decided to exploit the bug, they could cause some reasonable loses to the service.
I saw a scenario where a service refused to listen to someone who had discovered a bug, claiming they had no bug bounty. Some months later, a bad act discovered the bug and exploited it. The service suffered huge losses as a result.