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
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Next.js version: 15.4.7
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Router: App Router
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Production URL:
https://paideia-sigma.vercel.app -
Framework detected: Next.js (auto-detected after removing vercel.json)
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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.
