Next.js 15 Build Succeeds but Deployment Fails with "Unexpected Error"

Hi Vercel Team,

I’m on the Hobby plan and deploying a Next.js 15 project using pnpm and Prisma with Supabase as the backend.
Problem:

  • next build completes successfully
  • Static pages and serverless functions are generated
  • Deployment ends with:

An unexpected error happened when running this build. We have been notified of the problem.

Build Details:

Framework: Next.js 15.4.4

Package manager: pnpm

Database: Prisma + Supabase

Node.js version: 22.x (also tried 20.x)

Postinstall: prisma generate (works fine)

Relevant Logs:
[08:08:38.720] Route (app) ...  ✓ Generating static pages (31/31)
[08:08:39.405] Created all serverless functions
[08:08:39.684] Build Completed in /vercel/output
[08:08:39.803] Deploying outputs...
[08:08:46.023] An unexpected error happened when running this build.

What I’ve tried:

Locked Node version to 20.x in package.json

Verified local production build works (pnpm build && pnpm start)

Confirmed environment variables are correctly set for Supabase and Prisma

It seems like a deployment-stage issue since the Next.js build completes without errors.

Can you please help check what could be causing the unexpected error during final deployment?

Thank you!

Duplicate of Next.js 15 Build Succeeds but Deployment Fails with "Unexpected Error"