Cubik Studio

Currently, I am trying to convert my prior blockbench models to Cubik models so I can reduce the lag from my current models. I can do everything through cubik. I can import the .json into it. then do the lightning with the x to reduce the faces. I exported the model and then saved the texture. put them both into my pack and when I do it the model shows up but has the errored black and purple texture on it. What is the issue with this and why does this happen? How can I fix it?