There are two ways to gain a higher card balance, cash balance and bonus balance. Cash balance is gained when you load the card with money. Cash balance does not influence the basket value. In contrast, bonus balance is granted as a discount, and reduces the basket value. Depending on your card program configuration, the bonus balance is either applied to the same buy, or spent at a later time. Both, cash balance and bonus balance, reduce the amount to pay.
In order just to collect bonus balance, you only need to pass the card to the idents array of your Smart Transaction. The bonus is collected automatically, when the transaction is started, and the payment is executed. Only the card program must be configured for it, and the recorded revenue must be eligible for bonus. You can configure a blacklist or whitelist for articles to consider. You can even grant or forbid bonus collection for loading the card with cash balance. And you can control whether the bonus is applied to the full or to the reduced prices. More in the next sections.
How you spend bonus balance is explained in the section on payment.