Help needed: texture turns black in CAS and in game

Hi everyone,

I tried looking through the other threads for some help but couldn't find a solution for my exact problem. So recently I took up the project of converting Kalino's Dragon Package for Large Dogs to work for cats (for my own use). I was able to convert everything else just fine, however, because they don't have a texture for this asset in their project I tried to create my own. Everything seemed to work fine in blender:



and even in the swatches menu in Sims 4 Studio:



however once in game or in the CAS screen they just turned black:



I am new to making custom CC so I don't really know how to fix this. Maybe it has to do with the texture's placement? I don't know for sure...any help would be greatly appreciated!

Here are the files:
package: mega.nz/file/sDwwiYgR#nGwvb2eU_P4D68uq_uc0eUHzCc-FbcFeYn0xtcuis4U
blend: mega.nz/file/8epQUYYD#uiEnXIAL1qiVakzcbwsD2M8hlxs51rOI3avkOC-LvSE

Also I only made a diffuse texture for the spikes/fin and I based the mesh import off of the CatFinTail cc by sai1orrabit (https://sai1orrabbit.tumblr.com/post/180828693911/ts4-fin-ears-and-fish-tails-for-cats-maxis-match)

Thank you for your time and I hope someone can spare me some guidance x~x