Socket.io React App: Access to XMLHttpRequest at 'https://myserverURL/socket.io/xyz' from origin 'https://.mynetlify.app' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource

[nathanmartin]

@ryanh797 See my response here, as the core of the answer applies to you:

Site deploys fine, but backend/database data is not loading

@ketz555 Checking the repository that you’ve linked to, I can see that npm run start:backend executes nodemon server.js and the server.js file starts an Express server. You won’t be able to do this on Netlify, as it’s not how the hosting environment is intended to be used. The static portion of your application builds via CI and deploys to CDN, and then any runtime server side functions (or API’s) that you integrate with must either be running elsewhere, or be implemented via Serverless functi…

You cannot just upload and run a socket server with Netlify, you would need to host it elsewhere.