Server Action 405 Error on Static Pages - Reproduction

This reproduction demonstrates an issue where Server Actions return 405 on Vercel when used on statically generated pages.

Test Pages

• /docs/getting-started - Static page (force-static) - Should fail with 405 on Vercel
• /docs/quickstart - Static page (force-static) - Should fail with 405 on Vercel
• /dynamic-page - Dynamic page (force-dynamic) - Should work correctly

Expected Behavior

Server Actions should work on statically generated pages. According to:

• PR #51534 - fix: server actions initiated from static pages
• PR #63978 - fix server actions not bypassing prerender cache

Actual Behavior

On Vercel deployment, submitting a form with a Server Action on a static page returns:

405 Method Not Allowed

The request has the correct next-action header but the static page rejects the POST.

Environment

• Next.js 15.5.9
• React 19
• Deployed to Vercel
• Works correctly in local development