Custom biome 1.21.5 formatting help

I've been trying to test making custom biomes for 1.21.5 but they're failing validation.
The attached biome was made with the misode biome generator: https://misode.github.io/worldgen/biome/?version=1.21.5
When this failed I was recommended to take out the   "exit_type": "none", entry which I did and this didn't make a difference.
I don't know what I've done wrong here. Everything looks correct, and I made sure to make the .zip by highlighting data and pack.mcmeta  and sending to zip archive.
Also, I'm a complete idiot at coding, I don't know how to do it. I just use generators like this lol. Any help would be appreciated!
Note: this is just for custom biome colours in a WorldPainter project. No actual generation needs to take place with this biome.