Many modern slots offer a "buy feature" (or feature buy) that lets you pay a fixed multiple of your stake — often 100x — to trigger the bonus round instantly instead of waiting for it.
The trade-off
Buying guarantees the bonus, but the cost is high and results are still random — you can pay 100x and win less. Bought rounds often have a slightly different RTP than the base game. It is a fast, high-variance way to play. Only use it with a bankroll that can absorb several losing buys, and check the cost first.