Hey everyone 👋,

We’re building a Next.js app and our /api/user/create route works perfectly in local dev — it creates a MongoDB user, hashes the password with bcryptjs, and returns 200.

But on Vercel, the same route gives us:

• ⛔ 500 Internal Server Error (delayed ~1.8 seconds)
• We’ve already:
  • ✅ Whitelisted 0.0.0.0/0 in MongoDB Atlas
  • ✅ Verified MONGODB_URI is correct in Vercel env vars
  • ✅ Logged process.env.MONGODB_URI in the route and confirmed it loads
  • ✅ Route connects successfully locally and returns 200 every time
  • ✅ Used console.log() and console.time() to confirm that the error occurs after reaching MongoDB in production

We're using:

• mongoose for DB connection (lib/mongodb.ts)
• bcryptjs for hashing
• App Router with app/api/user/create/route.ts

We’re even returning the error stack trace in production and still just get a generic failure. Logs on Vercel don’t show the error clearly due to retention limit.

Any ideas why Vercel would fail where localhost succeeds?

Thanks in advance — we're stumped and happy to post snippets if needed!