Q.purple lantana was fully bloomed then in a day all flowers died
There are no other details; one day the plant was beautiful, the next all the flowers were dead. If this happened before I never noticed, which is unlikely.
The leaves are healthy.
This can happen with excessive heat, or dry weather. I would not worry too much, unless you are seeing other symptoms. It will likely bloom again once you trim the dead flowers. This article will help you with the care of these: https://www.gardeningknowhow.com/ornamental/flowers/lantana/lantana-plants.htm