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

Help
1

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!
3

Do you have all the environment variables added in project settings? If any are missing, that could cause a connection failure and lead to a deployment error.

They should be added automatically if you’re using an integration. Otherwise you’d need to add them yourself.