Why isn't my Vercel app able to receive JSON file from API hosted on Render

Question

This is how I'm implementing CORS on my backend

const allowedOrigins = ['http://localhost:3000', 'https://(myvercelapplink).app'];
app.options('*', cors());
app.use(cors({
    origin: function(origin, callback){
      // allow requests with no origin (like mobile apps or curl requests)
      if(!origin) return callback(null, true);
      if(allowedOrigins.indexOf(origin) === -1){
        var msg = 'The CORS policy for this site does not allow access from the specified Origin.';
        return callback(new Error(msg), false);
      }
      return callback(null, true);
    },
    credentials: true
}));

This is my vercel.json file in frontend. I have used rewrite because I'm using react router.

{
  "rewrites":  [
    {"source": "/(.*)",
    "destination": "https://(mybackendlink).com"
  }
  ]
}

I'm trying to login using google & after a successful login, I run an api called user-details which fetches my user data to the frontend.

But the request is 'pending' when I run it on Vercel, but it works fine on localhost. networks screenshot