Fix CORS preflight blocked
CORS preflight (OPTIONS) requests fail when the server doesn't return proper Access-Control-Allow-* headers. Browsers block the actual request.
Common causes
- Missing Access-Control-Allow-Origin.
- Preflight not handled (OPTIONS).
- Credentials mode without Allow-Credentials.
How to fix
- Add CORS headers to OPTIONS responses.
- Allow the requesting origin (or * for public APIs).
- Use CORS Checker to test.
Use our tool
Test CORSRelated