In order to cash out a bonus, you must meet the wagering requirement. This means that you have to 'wager' the bonus a certain number of times. It does not matter if the bet is profit or loss.
You have received a bonus of €10 and the wagering requirement is X10 with an expiration date of 30 days. This means you must wager €10 x 10 (a total of €100) within 30 days in order to cash out the bonus.