Why does my React app work locally but fail with CORS after deploying?
Because your local proxy bypassed CORS, but the production backend is not configured to allow your frontend domain. Always test CORS after deploying, not just on localhost, and configure the production backend's CORS headers.
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More FAQs in CORS in Production vs Development: What Changes for React Apps
In development, you use a proxy or extension to bypass CORS locally. In production, you must configure the backend to return the right CORS headers for the frontend domain, or serve both from the same origin to avoid CORS entirely.
Serve your frontend and backend from the same origin. Many production setups proxy API calls through the same domain, so there is no cross-origin request and no CORS issue at all.
Because with cookies or auth tokens, the server must set specific origins, not a wildcard, and Access-Control-Allow-Credentials must be true. A wildcard with credentials is blocked by the browser for security.
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