Max bet is a per-stake cap written into the bonus terms that applies for as long as the bonus and its wagering are active. The cap is usually noticeably lower than a player's normal stake, and that is precisely why exceeding it is the most common way to lose a bonus.
Why the rule exists
Without an upper cap a player would put the whole bonus on one large stake: a win would cover the wagering in one go, a loss would be the casino's money. The restriction forces turnover to accumulate in small stakes, where the house edge has time to work. The logic is understandable — the problem is enforcement.
Where players most often come unstuck
- Most casinos do not block an oversized stake. The spin goes through, the game continues and the bonus is voided only afterwards, often together with all bonus winnings. - The rule can extend to real money too when balances are mixed. Read in the terms which money enters play first. - Buying a bonus feature, tournaments and some of the casino's own original games are often forbidden entirely while a bonus is active. - Auto play offers no protection: if the stake changes in between, the responsibility stays with the player.
What to do
Open the bonus terms, search for the words "max bet", write the number down and keep the stake field below it for the whole of the wagering. Take a screenshot of the terms — in a dispute it is the only thing that speaks for you. Be sure to look at game weighting too, because those two rules always apply together, and check the small print of every offer on the offers page before you accept a bonus.