I’m using HDRP 4.20 (the latest 2018.3 release). I added a grass texture to the terrain details, if I use “Billboard” it doesn’t show up, if I don’t, it shows up but it’s pink.
You may change default billboard shader code. But
I think you should just wait.
Grass is closely related to patch. It is already stated that the roadmap will recreate the patch curling side (the existing method is definitely a problem) and I think it will change soon anyway.