VanillaPlus/temp/blockmodels/vertical_red_sandstone_slab.json

{
  "parent": "vplus:block/vertical_slab",
  "textures": {
    "bottom": "minecraft:block/red_sandstone_bottom",
    "top": "minecraft:block/red_sandstone_top",
    "side": "minecraft:block/red_sandstone"
  }
}