Bonus or promotional codes, are short codes made up of numbers and/or letters.
Some Casino bonuses require that you enter a specific code to qualify for the offer.
Most of the time, the Casino will have the code displayed on the website so that you can easily find it, copy it and enter it into the respective field.
You can also find bonus codes on affiliate websites and casino reviews. These usually have the codes for all the Casinos listed, as well as details of the promotions and what bonuses you can claim.
