All Next.js 15 App Router dynamic API routes return 404 on Vercel

Help
1

I’m experiencing an issue where all dynamic API routes in my Next.js App Router project return 404 on Vercel, despite building successfully and appearing in the Functions list.

Environment

  • Next.js version: 15.4.7

  • Router: App Router

  • Production URL: https://paideia-sigma.vercel.app

  • Framework detected: Next.js (auto-detected after removing vercel.json)

  • Local development: Works perfectly with npm run dev

Current behavior: On Vercel, all dynamic API routes (/api/[param]), e.g. /api/quiz/4w4EHpNCtGXv0CDCM52T and /api/test-dynamic/123, return the static 404 page (X-Matched-Path: /404) with no function logs. Static routes like /api/health and /api/test-simple work.
Expected behavior: Dynamic API routes should match their functions (they’re listed in Functions) and return JSON.
The pattern is clear: routes without dynamic segments [param] work fine, but any route with a dynamic segment returns 404.

Steps to reproduce:
Hit https://paideia-sigma.vercel.app/api/health → 200 JSON.
Hit https://paideia-sigma.vercel.app/api/test-dynamic/123 → 404 page, X-Matched-Path: /404, no logs.
Same for /api/quiz/.
Key observations:
Routes work perfectly locally with npm run dev
Routes appear in the Functions list in Vercel dashboard
Build logs show successful compilation
Response headers show X-Matched-Path: /404
No function execution logs are generated when accessing dynamic routes on Vercel
Removed vercel.json - no change
Middleware only matches /admin/*

Why would all dynamic API routes return 404 while static routes work, despite successful builds and the routes appearing in the Functions list? Is this a known issue with Next.js 15.4.7 or is there a configuration problem I’m missing?

and ofc the routes work perfectly locally with npm run dev. Let me know if there are any questions, I vibe coded this so I will try my best to answer. This is also my first deployment so I’m learning as much as I can.

2

There’s another community post with 404 debugging tips that might be helpful. Please give these solutions a try and let us know how it goes.

A human should be around soon to offer more advice. But you can also get helpful information quickly by asking v0.

5

In each dynamic API route file:

export const runtime = "nodejs";   // <-- FORCE serverless/node

Redeploy → dynamic routes should immediately start working.

If still broken –> Disable file-system dynamic route prerendering

export const dynamic = "force-dynamic";

Redeploy → test again.

6

This is expected behavior, [param] will only catch a single segment so it should work for /api/quiz but not /api/quiz/id

/api/[...segments] should be the route pattern you’re looking for

8

Tried, it didn’t work :frowning:

9

Yes, but in my app I’m accessing quizzes by ID via /api/quiz/[id]. For example: /api/quiz/4w4EHpNCtGXv0CDCM52T.

I should’ve specified, I’m not trying to match /api/quiz without an ID, only /api/quiz/[id]. My problem is even though there are no segments after id, it still doesn’t work with just /api/quiz/[id] and it’s driving me crazy.

Locally, hitting /api/quiz/4w4EHpNCtGXv0CDCM52T works; on Vercel it returns the static 404 page (X-Matched-Path: /404) with no function logs, even though this route is listed in Functions.

I tried something new:
The App Router handler is a catch‑all at the end of the path: src/app/api/quiz/[…segments]/route.ts with:

export const runtime = 'nodejs'
export const dynamic = 'force-dynamic'
export const dynamicParams = true

export async function GET(_req: Request, { params }: { params: { segments?: string | string[] } }) {
  const segments = Array.isArray(params.segments) ? params.segments : params.segments ? [params.segments] : []
  const sessionId = segments[0] ?? ''
  if (!sessionId) return Response.json({ error: 'Session ID is required' }, { status: 400 })

  // …load quiz by sessionId…
  return Response.json({ sessionId })
}

This route is listed in the Functions tab for the deployment as /api/quiz/[…segments].
Locally (npm run dev), /api/quiz/4w4EHpNCtGXv0CDCM52T works.

On Vercel (https://paideia-sigma.vercel.app/api/quiz/4w4EHpNCtGXv0CDCM52T), it returns the static 404 page (X-Matched-Path: /404) and no function logs.

I’m not hitting /api/quiz without an ID; only /api/quiz/{id}. Static APIs like api/health work; any dynamic API (/api/quiz/{id}) 404s the same way.

Given the catch‑all is at the end of the path and the route exists in Functions, why is router resolving /api/quiz/ to /404 on this deployment?? Thank you

10

Try to debug it with log, put some logs in same route and check that in vercel logs, I hope this will help you to debug the exact issue on live url.