There can be two reasons why this happens:
The pill box has run out of battery, plug in the charging cable and it will start flashing green and the white light on the top of the pillbox will start to flash at the dosing time.
The app needs to understand that the box has been re-filled. Follow the guide here and the lights will start to light up at the next dosing time.
If you notice that the pillbox only lights up when the charging cable is connected, please contact support and we will help you.