Currently this tool only works for picoCAD models. If you’re trying to paint/texture other 3D models I recommend blender, substance painter, or zbrush!
picoCAD has a complexity limit so if your models are complicated they won’t work correctly. The nice thing about blender is that it’s free so there’s no harm trying. Find a tutorial on just texture painting a similar object to what you want and watch it once and then follow it completely.
i tried blender but i'm kind of overwhelmed with the huge amount of options, which makes it complex/confusing for me. one wrong click somewhere and everything messes up later.