For context, I love "Retro Bowl", another game by this developer, so I immediately paid $3.99 for the ad-free version of this game to support them. Unfortunately, the rest of the game is set up to keep making you shell out cash, which made me quit pretty quick. Bad job, devs!
Here's how it works: To participate in games you need "energy" which you get by purchasing energy drinks. When you start, you get paid around $20 - $25 per game, and an energy drink costs $20. So you'll make about $5 profit per game if you're doing well. You can just barely compete in the minors with basic equipment, but to compete in higher leagues, you need to upgrade your equipment.
Upgrading your equipment costs several hundred dollars, and all the upgrades are temporary and only work for 10-25 games. I hated this mechanic, but figured I'd be able to afford the better stuff once I had won some games and was making more money. I won a few games, renegotiated my contract, and was suddenly making $60 a game. That's when I noticed that energy drinks now cost $50.
So you are purposely prevented from making meaningful progress in-game without spending real money. To upgrade from your most basic equipment to the next tier would require playing dozens of games, and then those upgrades would only last for 30 games or so. Or you can just spend $5 to get a few thousand bucks in-game!
Bad job guys. I won't be supporting this studio anymore.