CORS Preflight Request Failing
Frontend makes a complex request (POST with JSON body) to API, preflight OPTIONS request fails with 403 or 405 error. Actual request never sent because browser stops at preflight check. Simple GET requests work but POST/PUT/DELETE fail.
CORS configuration exists but doesn't handle preflight requests correctly.
Error Messages You Might See
Common Causes
- OPTIONS method not allowed in CORS configuration
- CORS headers missing or misconfigured: Access-Control-Allow-Methods
- Custom headers not whitelisted: Access-Control-Allow-Headers
- Credentials not allowed: Access-Control-Allow-Credentials missing
- Origin not in allowed list for preflight
How to Fix It
Ensure OPTIONS requests are handled and return 200 with CORS headers. Configure: Access-Control-Allow-Methods: GET, POST, PUT, DELETE, OPTIONS. Access-Control-Allow-Headers: Content-Type, Authorization. Access-Control-Allow-Origin: * (or specific domain). Access-Control-Allow-Credentials: true (only if credentials needed). Test preflight: curl -i -X OPTIONS http://api.example.com/endpoint
Real developers can help you.
Tejas Chokhawala
Full-stack engineer with 5 years experience building production web apps using React, Next.js and TypeScript.
Focused on performance, clean architecture and shipping fast.
Experienced with Supabase/Postgres backends, Stripe billing, and building AI-assisted developer tools.
Matthew Jordan
I've been working at a large software company named Kainos for 2 years, and mainly specialise in Platform Engineering. I regularly enjoy working on software products outside of work, and I'm a huge fan of game development using Unity. I personally enjoy Python & C# in my spare time, but I also specialise in multiple different platform-related technologies from my day job.
ISHANTDEEP SINGH
Senior Software Engineer with 7+ years of experience in React, JavaScript, TypeScript, Next.js, and Node.js. I’ve also worked as a tech lead for startups, owning end-to-end technical execution including architecture, development, scaling, and delivery. I bring a strong mix of hands-on coding, product thinking, and technical leadership, and I’m comfortable building products from scratch as well as improving and scaling existing systems.
Vlad Temian
15+ years shipping production infrastructure for startups. Former CTO at qed.builders (acquired by The Sandbox).
Cursor ambassador and agentic tooling builder.
I've scaled systems, automated deployments, and built observability tools for AI coding workflows. I specialize in taking vibe-coded apps from broken prototype to production-ready: fixing Supabase auth/RLS, Stripe integrations, deployment pipelines, and cleaning up AI-generated spaghetti.
I build tools in this space (agentprobe, claudebin, micode) and understand both sides: how AI generates code and why it breaks.
https://blog.vtemian.com/
Costea Adrian
Embedded Engineer specilizing in perception systems. Latest project was a adas camera calibration system.
BurnHavoc
Been around fixing other peoples code for 20 years.
prajwalfullstack
Hi Im a full stack developer, a vibe coded MVP to Market ready product, I'm here to help
Stanislav Prigodich
15+ years building iOS and web apps at startups and enterprise companies. I want to use that experience to help builders ship real products - when something breaks, I'm here to fix it.
hanson1014
Full-stack developer experienced in fixing and deploying AI-generated apps from Lovable, Bolt.new, Cursor, and Replit. I specialize in debugging Supabase integration issues (auth flows, RLS policies, database connections), fixing broken deployments, resolving routing/blank screen problems, and cleaning up messy React/Vite codebases. I also build production apps with the Claude API and have shipped a Mac desktop dev tool (Nexterm from scratch. Based in Hong Kong, fast turnaround.
Krishna Sai Kuncha
Experienced Professional Full stack Developer with 8+ years of experience across react, python, js, ts, golang and react-native. Developed inhouse websearch tooling for AI before websearch was solved : )
You don't need to be technical. Just describe what's wrong and a verified developer will handle the rest.
Get HelpFrequently Asked Questions
What is CORS preflight?
For non-simple requests (POST with JSON, custom headers), browser sends OPTIONS first to check if request allowed. If OPTIONS fails, actual request never sent.
How to allow all origins?
Access-Control-Allow-Origin: * allows all. For credentials, use specific domain: Access-Control-Allow-Origin: https://example.com
What headers must be allowed?
At minimum: Content-Type. Also: Authorization if using tokens. Declare with: Access-Control-Allow-Headers: Content-Type, Authorization