What "free spins bonus" comes down to is simple: spins are worth less than they sound. Free spins are the most common casino offer and the hardest to value at a glance. Each spin has a fixed stake set by the casino, often the smallest the game allows, and the winnings may land as cash or as a bonus with wagering. The number of spins in the headline says little until the spin value, the selected games and the terms on winnings are known.
Winnings from free spins usually arrive as bonus funds with their own wagering requirement, often counted on the winnings alone. Some offers pay spin winnings as cash with no wagering at all, and those offers tend to give fewer spins. A requirement on small winnings can still take a long session to clear, and the balance may run out first. The terms state which of the two applies, usually in the line that describes the spins.
A cap on free spin winnings limits how much the spins can turn into, however well they land. Anything above the cap is removed when the bonus converts to cash. Caps are common on spins given without a deposit and can be low enough to make a large hit on the selected slot pointless. The figure is part of the offer terms and matters most on volatile games, where the rare big result is the main reason to play.
Many offers cap spin winnings, especially spins given without a deposit, and anything above the cap is removed when the bonus converts to cash.
Multiply the number of spins by the stake of each spin; a hundred spins at the lowest stake can be worth less than twenty at a higher one.
The casino fixes it in the offer terms, often at the smallest stake the game allows, sometimes stating it only as a coin value.
Larger offers are often split by day, each batch needing a login or fresh opt in, so a missed day can mean a lost batch.
Usually as bonus funds with their own wagering, though some offers pay spin winnings straight into the cash balance.