To trigger the Bonus game, the number must have a Bonus icon attached to it. The Fortune Roulette Bonus Game is played on a 5x3 grid, and on every spin, a couple of multipliers will show up in random positions. If you land a Chest at the same time as coins, it will collect their values and add them to the win. Otherwise, the coin values are lost.
The round has five spins, but for every three Chests you land, +5 spins are added on top of the remaining ones. Collect six Chests and the coin values will get increased 5x, plus you get +5 spins. Finally, collect nine Chests and the Coin values are increased by 10x.