Can you try to be a little bit clearer on that! Do you mean that your prefabs appear pink? Most likely you are using the wrong pipeline, Rocky Hills Environment - Mega Pack (no SRP) is made for the Built-in render pipeline, not URP. Rocky Hills Environment - Mega Pack (SRP) is made for the URP and HDRP pipeline with the default pipeline being URP. Post some screenshots! Here's the fix for URP if you are using this pipeline. Just install this over your URP project!