Trying to make a custom biome - 1.20.1

Every time I try, not matter what code I use or how much I dumb it down, it does not work, and keeps giving me the error in the screenshot. Current ZIP file does not need any extracting, and is a bare-bones only adds basic biome file and it still fails. Does anyone have a working datapack I can reverse engineer/does anyone know what's going on here?