v0: environment variables missing on the published app (Vercel Production)

Short answer: v0 deploys to Vercel, and a variable only reaches a deployment if it is set for the Production environment and a new deployment is made after you save it. Add the variable in Vercel for Production, then publish again from v0.

Why it happens

v0 deploys projects to Vercel. Working branches get preview deployments, while publishing updates the Vercel project's production deployment and stable production URL.

Environment variables are key-value pairs configured outside your source code. Any change you make to environment variables is not applied to previous deployments; it only applies to new deployments. So a variable you add now does nothing to the build that is already live.

Each variable also has environments. Production applies the variable to your next Production Deployment. Preview applies it to your next Preview Deployment. A variable set only for Preview will not be there in Production.

Client-side environment variables must be prefixed with NEXT_PUBLIC_ to be accessible in browser code. If the prefix is missing, browser code cannot read the value.

How to fix it

1. Open your v0 project menu, then go to Settings → Environment Variables to add your own variables.
2. If the value comes from a database or other integration, check Project menu → Settings → Integrations. Adding an integration provisions a new user account on that service and adds the necessary environment variables to your project.
3. Open the deployment's inspector link from the deployment card in v0. The inspector is where you manage the Vercel project, including environment variables for Production, Preview, and Development.
4. In Vercel, add or edit the variable and select the Production environment for it. Choose Config or Secret for each variable: Config values stay readable to authorized members, Secret values are write-only after saving.
5. If the value is used in browser code, name it with the NEXT_PUBLIC_ prefix, for example NEXT_PUBLIC_API_BASE_URL.
6. Publish again so a new production deployment is created. In v0, open Publish, review the production deployment and selected domain, then select Publish Changes.
7. If the build fails, select Fix with v0 or Fix Build on the deployment card. v0 reads the relevant logs, diagnoses the failure, and applies a fix.
8. To work locally with the same values, run vercel env pull to create a .env file with the variables from your Vercel project's Development environment.

How to check it worked on your live app

1. Open a private window so you are not signed in with an old session.
2. Use a fresh email address if the app asks you to sign up.
3. Go to the stable production URL and do the action that was failing, such as loading the page or feature that reads the variable.
4. If it still fails, open the deployment card in v0 and check the build logs and errors, then confirm the variable is set for Production and that you published after saving it.

Prompt to paste into your AI builder

Paste this into your AI builder: "My published app is missing an environment variable in Production on Vercel. Show me first, before changing anything, every place in the code that reads this variable, and tell me whether it is read in browser code. If it is read in browser code, rename it with the NEXT_PUBLIC_ prefix and update every use. Then list the exact variable names I need to set in Vercel for the Production environment, and tell me to publish again after I save them."

FAQ

Why does it work in the preview but not on the live site? Preview deployments are built from working branches and have unique URLs. Production deployments serve the project's domains. A variable set only for Preview is applied to your next Preview Deployment, not to Production.

I added the variable. Why is the live app still broken? Changes to environment variables are not applied to previous deployments. They only apply to new deployments, so you need to publish again.

Where do I add my own variables in v0? From Project menu → Settings → Environment Variables. You can also manage them in the Vercel project through the deployment's inspector link.

Why can't my browser code see the value? Client-side environment variables must be prefixed with NEXT_PUBLIC_ to be accessible in browser code.

Are variables shared across chats? Environment variables are project-scoped, so all chats in a project have access to the same environment variables.

Related guides

• Works in the preview, breaks after deploy: the 4 differences that cause it — covers the preview-versus-production gap that hides missing settings.
• A button on my app stopped working after I published it: why, and how to fix it — for a single action that fails only on the live site.
• My app is stuck loading after I publish it: why the spinner never stops, and the fix — when a missing value leaves the page waiting.

Sources

• Deployments | v0 Docs
• Databases | v0 Docs
• Environment variables | Vercel Docs
• Full-stack apps | v0 Docs
• Environment Variables | v0 Docs

VibeFix's AI agent signs up to your live app like a new person and shows whether sign-up and your pages work. It may not show v0 preview works but the published app lacks variables directly. VibeFix checks; it does not fix your app.

Last checked: 19 October 2026, against the sources listed above.

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