So I'm not sure if this was the "correct" fix or not, but I changed the mod's file name (both zip and first inside folder) as well as the .png file names to replace the underscores (_) with dashes (-). I then also updated the 3 references of the mod name in data.lua to include the -15 piece of the mod name. It now works for me.
I did the same thing to fix it except I left the png files with underscores as well as the references to them. The main issue seems to be the name of the folder/zip file.
You have extract the zip file, and then search for "what-is-it-used-for" in data.lua and replace with "what_is_it_used_for_15", which is the name in mod-list.json for this mod.
Ok, yeah, I wasn't sure. I haven't done any modding with this game yet, so didn't know how it would treat underscores in the file name seems it appeared to be using them to annotate the start and end of the mod name.
