What I don’t see here is the parameter for your grass node. So without knowing what you did I will try to help. I don’t think you assigned anything to the grass node.Left click on the grass node. In the left hand pain you need to assign something to your array. Click the “+” next to “array elements”. then in the spot that opens you will give it a name and then put the material in the box provided. I have attached a pic to show you what I mean.
