I'm trying to add creeper spawn in deltas, but I don't understand why they don't appear, everything seems logical

[
{
"mob": "minecraft:creeper",
"dimension": "minecraft:the_nether",
"biome": "minecraft:basalt_deltas",
"result": "allow"
}
]

Please read the wiki. It clearly states (in the FAQ) that you cannot use spawn.json to add spawns. To add spawns you need to use spawner.json. Note that spawner.json has a completely different syntax.

Thank you, I figured it out and now everything works с: