Local API server failing with CORS error when connecting to CodeSandbox preview

[MischiefBrew]

I am running a local Node.js backend API on my machine at localhost:5000 and trying to fetch data from it inside my frontend CodeSandbox project.

The request fails with the console error: Access to fetch at 'http://localhost:5000/api' from origin 'https://xxxx.csb.app' has been blocked by CORS policy.

How do I resolve this cross-origin issue in this environment?

[AnouarMohamed]

const express = require('express');
const cors = require('cors');
const app = express();

app.use(cors({
  origin: 'https://xxxx.csb.app', // Replace with your sandbox preview URL
  credentials: true
}));

CodeSandbox previews run over secure HTTPS (csb.app), while your local API runs on unsecure HTTP. The browser blocks this cross-origin request by default.

To resolve this, configure your Express backend to allow the CodeSandbox origin:

1. Install the CORS middleware: npm install cors
2. Add it to your server configuration as shown above.