Just getting into the whole online casino thing and learned something kinda important—those bonus spins you get, they don't stick around forever. Like, say you sign up with Crush Wins Casino, they'll give you a window, something like 7 days, to use them up. If you miss that, it's bye-bye bonus.
Also, keep tabs on how much you're betting when you're playing with bonus cash. They have this rule where if you bet over the limit, you might lose your spins, or worse, what you've won.
Oh, and if you're winning, might be a good plan to just take the money and run instead of gambling it all trying to meet their betting rules. Sometimes it's smarter to lose the bonus than lose the cash you've won...