You cannot combine credit and discounts on the same ride.
When you have both the option to pay with your credit and a discount selected at the same time, the app will automatically apply whichever option benefits you the most.
Please, note that credit is valid exclusively for use on rides.
Additionally, credit and promotions have conditions that must be met for them to be applied (specific days of the week, payment method used), and they may also vary from month to month.