I have tried to deploy my React/Node.js project to Vercel. As client and server are placed on different URL, I have got a CORS problem. I had used cors library and different settings. In the end when I get some data from server (list of news) it works OK 7 in 10 times, other 3 times it shows me CORS error with same API. But when I try to log in or sign up it always shows CORS error.

I have tried to deploy my React/Node.js project to Vercel. As client and server are placed on different URL, I have got a CORS problem. I had used cors library and different settings. In the end when I get some data from server (list of news) it works OK 7 in 10 times, other 3 times it shows me CORS error with same API. But when I try to log in or sign up it always shows CORS error.