Hi @supergemhere. Did you add the headers in your Express configuration? It’s best to use the framework’s preferred strategy when one is provided since this prevents configuration conflicts.

Some people have found that Express CORS Middleware makes configuration easier. But there are many ways to configure your app.

I found some more resources that may help you get it working in your project:

• Add headers to the Express instance
• Configure the CORS stuff before your routes
• Handle the HTTP OPTIONS method before handling other request methods on the same route
• Pass “http://” before “localhost:”

It’s also worth reading to understand more about CORS if you're not already familiar. These pages can help you understand how it works so you can identify what’s going wrong.

• CORS - MDN Web Docs Glossary: Definitions of Web-related terms | MDN
• Preflight request - MDN Web Docs Glossary: Definitions of Web-related terms | MDN

Yes, I'm using the CORS lib from node and I managed it to work, actually everything was fine on local environment, the problem happens on the deployed version on the vercel, It kinda looks like it doesn't care about the CORS options written inside the index.js file, also I have read an article where there was said that vercel somehow overwrites the CORS.

Vercel respects the CORS headers you set in your application. If you've configured CORS headers in your code or in the vercel.json config, these will be preserved. There are some other headers that automatically get added to deployments, such as x-vercel-id, x-forwarded-host, and x-robots-tag. That may have the source of confusion for whoever wrote the article you found.

The preferred method is to set headers in your application code. But it's also possible to add headers in a vercel.json for the project. There's a guide listing the options and some examples here:

https://vercel.com/guides/how-to-enable-cors