/image flat design illustration showing a smart app interface on a smartphone screen. The app should display various credit card transactions in a clean, minimalist style with vibrant colors. Each transaction is represented by simple icons and short descriptions. At the top of the screen, there should be a clear, bold notification for an upcoming payment due date. The background of the image is plain to enhance the visibility of the app interface. The smartphone is modern-looking and placed centrally against a soft, neutral-colored backdrop.