I have a Mini-Famous Dark Blue Calibrachoa that was blooming well. The last couple of weeks it doesn't bloom at all, just have the green leaves hanging down.
If they're in a container or hanging basket, they normally require additional fertilizer. That said, the nitrogen content may be higher than it should which can limit the flowering. Phosphorus can help offset this. I would recommend adding a bit of bone meal to encourage more blooms. Here is more information: https://www.gardeningknowhow.com/ornamental/flowers/million-bells/calibrachoa-million-bells.htm