In the fine print it’s stated that “players must bet 3 credits to play bonus games.” That doesn’t mean three credits to activate the bonus.
Notice it does not call them “free” games. The signage on the machine shows that getting three scattered diamond or devil symbols on a three credit bet will award the player 10 “bonus” games that pay 3x. It’s a classic, 3-reel slot machine called Diamonds & Devils by Bally.
Here’s another older machine that’s still in existence.
