Each free money promo has a "wager requirement". It's usually a multiple of the promo credit amount. EG if they give you $20 in free money with a 10x wager requirement. You need to gamble $200 before you can cash out. Most of the promos have wager requirements like that. It's hard to cash those out because there's a good chance you will go broke long before you have fed 10x the promo money into the machine.
Promos with a 1x wager requirement are great, because they are basically a guaranteed payout. Even if you don't hit any jackpots, you're going to have an accumulation of small payouts you earned while getting to the 1x wager requirement. Just pick a penny slot, bet one credit per line, do auto spin the number of pulls needed to hit the wager requirement, cash out. Eg if you pick a penny slot with 30 lines, that's 84 pulls to get to $25 wagered.
I've managed to cash out about $200 this way so far. I've cashed out $80, $40, $30, and $20 a couple times. The site is still new and they are still in aggressive customer acquisition mode, so these will probably continue for a while yet.
But again, I need to reiterate, NEVER PUT REAL MONEY INTO THE SITE. Gambling from home is an easy way to lose tons of money you can't afford to lose, even if you set up your account with good restrictions. But free gambling money is there to be had if you pay attention, and can control yourself.
I usually cash out if I'm north of $20 and just keep playing if I'm under that. But you can set up your own cash out rules, SO LONG AS YOU NEVER PUT REAL MONEY INTO THE SITE.
The other $25 was a registration bonus that probably had different cash out terms and by cashing out before you satisfied them, you waved your rights to the remaining promo balance. Which is probably fine, because you could have lost everything before satisfying both requirements. Better to take the guaranteed $25.