I got myself 2 hibiscus plants 3 months ago, both growing well. One has flowered, the other is getting buds but they are empty.
If you mean the buds fall off without opening, this article will give you some ideas on what to look for as the cause. https://www.gardeningknowhow.com/ornamental/flowers/hibiscus/hibiscus-flowers-hibiscus-blossoms-falling-off-plant.htm
Also, you might want to adjust watering, light, or fertilizer. This article will give you some tips: https://www.gardeningknowhow.com/ornamental/flowers/hibiscus/how-to-care-for-hibiscus-plants.htm