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Unfortunately, your photo did not come through. I am unable to see the damage. Without a description of the environment, or a way to see where, how, and what it is planted in I cannot give a good diagnosis. I have to assume that its environmental or soil conditions are not met. Once you are sure that the area is suitable for their growth, then you can begin to diagnose the issue.

This article will help you to know what the plants require in order to be healthy:

https://www.gardeningknowhow.com/ornamental/flowers/lisianthus/growing-lisianthus-flowers.htm