I trusted and purchased it because I had received a lot of help from the free lectures in the past..!! Oh, but I took the teacher's free lecture and created a React website using the game company's open API and distributed it. I didn't use DB and just received API requests, processed them, and rendered them. After distributing it with Vercel, it worked well for a few days, but it stopped working properly because a CORS issue occurred. In this case, do I need to have a backend like nodejs?