The phrase "to add a bonus" means to provide an additional benefit or reward for something that has already been completed. It can refer to giving someone extra money, time off work, or other perks as a way of recognizing and appreciating their hard work or achievements. The term is often used in the context of employment, where employees may receive bonuses based on their performance or productivity. In general, "to add a bonus" means to enhance something that already exists by providing an extra incentive or reward for it.