Might want to check this out for your Resource Pack

It seems old-fashioned but from what I remember Paintings++ packs have to be more than a resource pack,

example from the default .json:
"paintings": [ { "name": "abstract_blue", "square": 16 }, { "name": "abstract_rainbow", "square": 16 }, { "name": "abstract_red", "square": 16 },

Okay, so I've learned more about the recent Paintings++ changes. Closing for now while I properly learn to reproduce. my apologies.