Most casinos have a wagering requirement for you to withdraw your winnings. As the OP said, you only need to wager with the amount that's given to your account for you to withdraw anything that's left.
You don't have to gamble with all of that winnings but try to balance it with any amount that you can gamble and prolong your stay until you're able to hit the wagering amount and you'll be finally able to withdraw that.
Well I also got the free bonus of 50 free spin and won 42$ worth of bonus but with what I read on the site would need to wager through a real deposit because I have tried playing with like what HONDACD125 was complaining but I took time to go through and saw that the total amount that would be withdrawable from the bonus of 42$ is actually about 1270$ which is approximately 30x wager requirements of the bonus of 42$ and for that's a really long shot to actually try winning 🤔.
That's a lot to ask for a $42 worth of winnings. If it's asking for a $1270 wager/deposit, that's too much because if it happens to me I'd just leave it there.
Although I've experienced in some other casinos that asked me as well with these wagers and I did complied through the usage of my winnings without any other deposits. Because wagering and deposit requirements are two different requirements.
If it only asks for a wager, that's all you gotta do but if it's asking for both, it's not worth it if that's the case with too much amount. Maybe the owner/developer can adjust that to maybe 1x or 2x because that's usually the wagering requirements are.