http

CORS Preflight Failure

CORS|cross-origin|Access-Control-Allow-Origin|preflight|OPTIONS

Fixes

1.Add CORS headers on the server: `Access-Control-Allow-Origin`, `Access-Control-Allow-Methods`, `Access-Control-Allow-Headers`
2.Ensure the server responds to OPTIONS preflight requests with 200/204 and the correct CORS headers
3.For credentials (cookies/auth), set `Access-Control-Allow-Credentials: true` and specify the exact origin (not `*`)

corspreflightcross-origin

Related Errors

404 Not Found — Debugging

404 Not Found|Cannot (GET|POST|PUT|DELETE)|Route not found

•Verify the URL path, method, and trailing slash — `/api/users` vs `/api/users/` may route differently
•Check that the route is registered — look for typos in route decorator or router config

500 Internal Server Error

500 Internal Server Error|InternalServerError|server error

•Check server logs for the full stack trace — the 500 response usually hides the real error
•Common causes: unhandled null reference, database connection failure, or missing environment variable

403 Forbidden

403 Forbidden|forbidden|insufficient permissions

•Check authentication token is valid and not expired — inspect the JWT payload at jwt.io
•Verify the user/role has the required permission for this endpoint in your authorization logic