Bonus abuse is when a member at an online sportsbook or casino joins just to take advantage of the bonus. They’ll withdraw and leave the moment they meet the playthrough requirements, meaning the casino basically loses money.
Honestly, it’s not as much of a problem now as it was when online betting sites were new. To avoid being accused of it, simply continue betting on the site. But the worst thing that will happen is that they’ll block you from logging in again.
If you meet the requirements, they have to allow a withdrawal. If they don’t, dispute it with the Illinois Gaming Board (IGB).