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Quick Fix Guide: Common Vercel Errors

Error: "Cannot find module 'better-sqlite3'"

What it means: You're trying to deploy the backend to Vercel (won't work)

Solution:

  1. Only deploy frontend to Vercel
  2. Deploy backend to Railway, Render, or VPS
  3. Update vercel.json with backend URL

Error: "ENOENT: no such file or directory, open 'bizmanager.db'"

What it means: SQLite database file doesn't exist (serverless has no persistent storage)

Solution:

  • SQLite is incompatible with Vercel serverless
  • Use Railway/Render/Fly.io for backend with persistent storage

Error: "No 'Access-Control-Allow-Origin' header present"

What it means: CORS is blocking requests from Vercel domain to your backend

Solution:

  1. Update backend .env: 
    FRONTEND_URL=https://your-app.vercel.app
  2. Redeploy backend
  3. Clear browser cache and try again

Error: "Failed to load resource: net::ERR_NAME_NOT_RESOLVED"

What it means: Invalid backend URL in vercel.json

Solution:

  1. Check vercel.json rewrites section
  2. Verify backend URL is correct and accessible
  3. Test backend URL in browser: https://your-backend.com/api/health
  4. Redeploy Vercel frontend: vercel --prod

Error: "Build failed" during Vercel deployment

Common causes:

  • Missing npm install in frontend directory
  • Build command running in wrong directory
  • Missing environment variables

Solution:

  1. Check vercel.json has correct paths: 
    "buildCommand": "cd frontend && npm install && npm run build",
"outputDirectory": "frontend/dist"
  2. Set environment variables in Vercel dashboard
  3. Check build logs for specific error

Frontend loads but can't login / API calls fail

Possible causes:

  1. Backend not running
  2. Wrong backend URL in vercel.json
  3. CORS not configured
  4. Backend requires environment variable not set

Debug steps:

  1. Open browser DevTools → Network tab
  2. Try to login
  3. Check failed request URL - where is it going?
  4. Check response - what error message?
  5. Test backend directly: curl https://your-backend.com/api/health

Solution:

  • If 404: Update URL in vercel.json
  • If CORS error: Update FRONTEND_URL in backend
  • If 500: Check backend logs for errors
  • If timeout: Backend may be sleeping (free tier), wait 30s and retry

Environment variables not working

Issue: VITE_API_URL not being used

Solution:

  1. Variable must be prefixed with VITE_ to be accessible in Vite
  2. Set in Vercel dashboard: Project → Settings → Environment Variables
  3. Must redeploy after adding variables: vercel --prod
  4. Variable should NOT include /api suffix if using rewrites in vercel.json

Backend works locally but not in production

Common issues:

  1. Environment variables not set on hosting platform
  2. Database not initialized (run npm run setup)
  3. Port conflicts (use process.env.PORT)
  4. Missing NODE_ENV=production

Solution:

  1. Check all env vars are set on hosting platform
  2. Check logs for specific error
  3. Ensure database file exists and is writable
  4. Verify persistent volume is mounted (Railway/Render)

Need More Help?

  1. Check full guide: VERCEL_DEPLOYMENT.md
  2. Check Vercel logs: vercel logs
  3. Check backend logs on your hosting platform
  4. Test backend health: https://your-backend.com/api/health
  5. Verify CORS: Should return Access-Control-Allow-Origin header

Recommended Architecture

Frontend (Vercel)
  ↓ HTTPS
Backend (Railway/Render)
  ↓
SQLite Database (persistent volume)

Do this: Split frontend/backend deployment Don't do this: Try to run SQLite on Vercel serverless