spawn.json

[
	{
		"dimension": 0,
		"mob": "minecraft:slime",
		"block": "minecraft:grass",
		"result": "allow"
	},
	{
		"dimension": 0,
		"mob": "minecraft:slime",
		"result": "deny"
	}
]

po...spawn.json

[
	{
		"dimension": 0,
		"block": "minecraft:grass",
		"mobs": [
		{
			"mob": "minecraft:slime",
			"weight": 5,
			"groupcountmin": 1,
			"groupcountmax": 3
		}
	]
    }
]

How to fix it?

Ps. minecraft:grass -> minecraft:grass_block still not spawning.

Try to remove the block condition on potential spawn

Try to remove the block condition on potential spawn

Removed, but the world still not spawning slime, also I changed minecraft:grass or minecraft:grass_block.

And, when I using the incontrol mod, I can't generate the new world, stuck in prepare spawn area 0%, until I delete the content in potentialspawn.json and spawn.json.