Mass placing grass objects

Hi! My problem is that I'm trying place my 3D grass by making it to "Detail Mesh" on Terrain's "Paint Detail" tool. When I start placing, nothing appears :( I imported my grass as *.fbx file and it doesn't have any texture on it. I have tried different brushes, brush sizes, opacity and target strength, but nothing works.

You can download my prefab from HERE if you want.

Thanks for help :)