I'm having trouble getting mobs to spawn in alternate biomes.

I am getting the below error:

''''
[main/WARN]: could not test biome config for alexsmobs:bone_serpent_spawns, defaulting to no spawns for mob

''''

Here is my json for the mob:

https://paste.gg/p/anonymous/e20dc3726f2046ea9dc76f383e8a8ec0

I have tried multiple different syntax formats, but none have worked. Could you please give me an example of how this file SHOULD be formatted in order for it to work?