When you are given a Welcome Bonus, you will find that they have playthrough requirements attached to them. What this means is that you will need to roll over the bonus money a certain number of times before you will eligible to withdraw it or any winnings that you have picked up. So, to give you an example, if the playthrough requirements are 5x and you have received 5,000 rupees as a bonus, you will need to wager 25,000 rupees before a withdrawal is possible.