My startup is almost near to fail

I with my friend built a mvp version of your tech product. It was unique and very helpful for students. We gained 500+ users in one week and done some small sales. But problem with our startup was that, it was really dependant to copyrighted material. The creators of those materials never give permission to use. They are an educational materials that includes book parts and audios. So as a founders, what would you recommend to do? So far there is no problem with our work but I feel like, in future there surely be.