In my opinion, the gambling site should have programmatically made it impossible to bet from the bonus account on the listed games and introduced the necessary limits. Otherwise it all looks very much like a not entirely honest business, with its creators covering their actions with a user agreement.
Unfortunately, this is very often the case and does not only affect online casinos. I know of a case where a user registered with an exchange via VPN and deposited
BTC. During the withdraw, his account was checked, it was determined that he had registered via VPN and his account was blocked with reference to the "user agreements" - he never saw the
BTCagain.
The platforms take advantage of the fact that hardly anyone of us actually reads the user agreements or terms and conditions and then have a powerful weapon at hand to confiscate funds etc. in the event of a dispute. This ofc would most likely not stand up in any court, but the effort for a lawsuit is hardly ever taken ...