The "Beach Shader" Trying to paint the Terrain_Mat onto imported geo

I downloaded the “Beach Shader” package (purchased from the marketplace). I noticed the sandy beaches has a material called Terrain_Mat. It appears black until you paint it using the landscape maker. Unfortunately, It appears it can only be painted onto geo generated with the Landscape tool. I have tried to paint it onto geo I imported but, I am not able to. Is anyone familiar with this shader? Do you know if this shader can also be applied to imported geo?
If so, could you tell me how.

Thanks in advance.