Flask + Server Functions - CORS - Help

Hey,

I'm currently deploy Flask app (Deployed as Serverless). I'm also having a React Vercel App.

At my Flask app, I have custom env (staging) with vercel domain, which Im using the bypass token for the frontend to interact with him.

I keep getting CORs Issue at my frontend (from chrome). I tried add flask-cors at the code itself, or alternative adding to vercel.json the following:

{
  "rewrites": [
    {
      "source": "/api/(.*)",
      "destination": "/api/index"
    }
  ],
  "headers": [
    {
      "source": "/api/(.*)",
      "headers": [
        {
          "key": "Access-Control-Allow-Origin",
          "value": "*"
        },
        {
          "key": "Access-Control-Allow-Credentials",
          "value": "true"
        },
        {
          "key": "Access-Control-Allow-Headers",
          "value": "*"
        },
        {
          "key": "Access-Control-Allow-Methods",
          "value": "GET,OPTIONS,PATCH,DELETE,POST,PUT"
        }
      ]
    }
  ]
}

both are not working.

Im also getting 401 at the preflight request when trying do OPTIONS request to the backend.

At postman everything is working. Am I missing something? Thanks!