Project Title: Fix Vercel Deployment Errors (404) – React + Next.js Serverless + Supabase (Razorpay Issue)

Project Description:
My website works perfectly on localhost (frontend, admin panel, APIs, and payment flow), but when I deploy it on Vercel, I start getting multiple errors, especially 404 errors and payment issues. I need the live site to function exactly the same as it does on localhost without breaking any features.

Tech Stack:

- Frontend: React (Vite)
- Backend: Next.js Serverless APIs
- Database: Supabase
- Payment Gateway: Razorpay + Manual UPI
- Admin Panel: Custom admin dashboard
- Hosting: Vercel

Current Issues on Live (Vercel):

- API routes returning 404 errors (e.g. /api/orders, /api/products, /api/health)
- Admin panel routes showing 404 on deployed domain
- Razorpay works perfectly on localhost but does NOT work on the live site
- Pincode API and some serverless functions fail on production
- Some API routes return HTML instead of JSON
- Possible environment variable and routing configuration issues
- Cross-origin and proxy-related problems after deployment

What I Need:

- Complete debugging of Vercel deployment
- Fix all 404 errors (frontend + API routes)
- Configure proper routing (vercel.json, rewrites, redirects)
- Fix Razorpay integration on live site (it works on localhost but not in production)
- Ensure all serverless APIs work exactly like localhost
- Proper setup of environment variables (Supabase, Razorpay keys, Admin API key)
- Fix CORS, proxy, and production API handling issues
- Make admin panel, orders, and payment system fully functional on the live domain

Important Requirement:
I want the website to be fully working on the live domain exactly like it works on localhost. No features should break, including admin panel, orders, APIs, and payment flow.

Access I Can Provide:

- GitHub repository
- Vercel project access
- Supabase access (if needed)
- Environment variables and configuration details

Preferred Freelancer:

- Strong experience with Vercel deployments
- Expert in Next.js serverless functions and API routing
- Experience with Supabase integration
- Razorpay payment gateway debugging experience

Budget: Open (Looking for a cost-effective solution)
Timeline: Urgent (1–3 days preferred)

Note:
The website is already built. I do NOT need new development. I only need an expert to fix deployment, routing, API, and Razorpay issues so the live site works 100% like localhost.