FixesVercel and Next.js errors and fixes
Deploys that fail or show a 404, function timeouts and size limits, environment variables, redirect loops, preview access and Next.js build and runtime errors. Each page is checked against Vercel’s or Next.js’s own docs and says what to try first.
14 Vercel and Next.js fixes. Also see Web app development.
- Vercel errorVercel function times out with a 504 (FUNCTION_INVOCATION_TIMEOUT)Vercel returns a 504 when a function doesn’t finish within its maximum duration, and that time includes sending the response. Find the slow call first: an AI or outside API with no timeout, a slow database query, or a database far from the function’s region. Then stream the response or move long work to a background job. Raise maxDuration last, within your plan’s limit.
- Vercel errorWhy does my Vercel Function return 413 FUNCTION_PAYLOAD_TOO_LARGE?Vercel caps the request body and the response body of a Vercel Function at 4.5 MB. If a file upload goes through your function, upload it from the browser straight to storage instead, for example with Vercel Blob client uploads. If the response is too big, return less per request or stream it. When you measure, remember the browser’s network tab shows the gzipped size by default.
- Vercel deploymentVercel environment variable is undefined in productionVercel applies a new or changed variable only to new deployments, so redeploy (a new build) after saving it. Check it’s enabled for the right environment, Production or Preview. And if the browser needs it, it must use your framework’s public prefix, such as NEXT_PUBLIC_ in Next.js, which also means it’s visible to anyone, so never put secrets there.
- Next.js and React errorNext.js hydration error: the server HTML didn’t match the browserFind what renders differently on the server and in the browser. Most often it’s a browser-only value read during render (window, localStorage, the current time, a random number): move it into useEffect, so the first browser render matches the server. If that isn’t it, check for invalid HTML nesting, such as a <div> inside a <p> or a link inside a link, then test in a private window without extensions.
- Vercel build errorVercel build fails with Module not found: Can’t resolve, but works locallyVercel says this error almost always means the casing in an import doesn’t exactly match the filename. Your Mac or Windows machine ignores the difference by default; Vercel’s Linux build doesn’t. Find the path in the Build Logs and make the import and the filename match exactly. If Git missed a case-only rename, rename through a temporary name with git mv. Otherwise check for a package missing from package.json or a wrong relative path.
- Vercel functions errorVercel FUNCTION_INVOCATION_FAILED (500 Internal Server Error)The function crashed while handling the request. Open the deployment’s Logs tab and find the error from the failing request. Typical causes are an error your code didn’t catch, or a setting such as an environment variable that’s missing in production. Fix that, wrap the handler in try/catch so it returns a real error response, and redeploy.
- Next.js build errorNext.js: “useSearchParams() should be wrapped in a suspense boundary”Move the code that calls useSearchParams() into a small Client Component and wrap it in <Suspense>. That keeps the rest of the page static. If the whole route should render on each request instead, call connection() in the Server Component page. To find the component, run next build --debug-prerender.
- Vercel deployment errorVercel “404: NOT_FOUND” on a deployment that says ReadyFirst open the .vercel.app URL. If it works and your own domain doesn’t, fix the DNS records. If both 404, check that the Framework Preset isn’t set to Other and that the Output Directory matches where your build writes files, then redeploy. If only dynamic routes 404, set dynamicParams or render them dynamically.
- Next.js build errorNext.js “DynamicServerError: Dynamic Server Usage”A function like cookies() or headers() from next/headers ran outside the call stack Next.js bound it to: inside a setTimeout or setInterval, or after a promise you didn’t await. Call it outside the timer or callback, then pass the values in. Await every promise that calls it.
- Vercel deployment errorVercel won’t deploy: the commit author isn’t the owner or a team memberOn a Hobby team, a private repo in a GitHub organization, GitLab group or Bitbucket workspace can’t deploy: make it public or move to Pro. Other private repos deploy only commits made by the team owner. On Pro, the commit author must be a team member: add or approve them, then redeploy. If Vercel can’t identify the author, check that the commit email matches a verified email on the Git account.
- Vercel domain errorVercel “ERR_TOO_MANY_REDIRECTS” with Cloudflare in frontA common cause is Cloudflare’s Flexible mode: in Cloudflare’s SSL/TLS settings, change Flexible to Full (strict), which needs a valid certificate on the Vercel side. If the loop continues after that, look for app redirects, Vercel domain redirects and Cloudflare rules that send the same address back and forth.
- Next.js image errorNext.js image error: the hostname isn’t configuredAdd the image’s address to images.remotePatterns in next.config.js, with the same protocol, hostname, port and path the src uses. In our experience you then need to restart the dev server or redeploy before the change shows. Most cases we see are a missing subdomain, such as storage or cdn in front of the domain.
- Next.js Server Action errorNext.js Server Action fails on uploads over 1 MBFor forms that are only a little over 1 MB, raise serverActions.bodySizeLimit in next.config.js and leave some room for the upload overhead. For real files, such as photos or PDFs, upload from the browser straight to storage and send only the file’s address to the Server Action. On Vercel, a function can’t take a body over 4.5 MB whatever the setting.
- Vercel access problemVercel preview link asks visitors to log in to VercelSend people the production domain, or a Shareable Link for the preview deployment. For tools such as tests or webhooks, use Protection Bypass for Automation with its secret in a header. Turning protection off makes every existing deployment public, so we keep it on.
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