By Partly fixable yourself. Read the log, add missing variables, retry.
- How serious
- Medium
- Fix it yourself?
- Partly, some steps need a developer
- Typical cost
- €99–$990 for a single fix (prices)
- Top rated for v0
- Afterbuild Labs · 10.0/10
What you see. You clicked Publish in v0 and the Vercel deployment card shows a build error instead of a live URL.
Why it happens
v0 generates a Next.js app and publishes it to a Vercel project. Vercel then runs next build on a clean machine. Code that ran in v0's preview can still fail here, because the production build type-checks every file and resolves every import. The two most common errors are a module not found, when a file was renamed or an import path has the wrong case, and a type error in a component the AI edited last.
The other big cause is environment variables. The preview had them, the Vercel project does not, so any code that reads a key at build time fails or renders empty. Vercel only applies new variables to new deployments. Rarer causes are an invalid vercel.json, which fails before any log exists, builds over the 45 minute limit, and memory above the 8192 MB build allowance. The build log almost always names the file.
Fix it yourself
- On the v0 deployment card, click Fix Build or Fix with v0 once. v0 reads the log and applies a fix. Repeated fixes may cost credits.
- If that fails, open Vercel, go to Deployments, click the failed one and expand Building. Scroll to the first red Error line, not the last.
- For a module not found error, check the file exists and the import matches its name exactly, including upper and lower case.
- For undefined keys, open Settings → Environment Variables in the Vercel project, add each variable for Production, then redeploy.
- If there are no logs, check
vercel.jsonfor a typo and that the commit came from a team member. - If the error only appeared after the last prompt, ask v0 to restore the earlier version, publish, and redo the change in smaller steps.
When to get an engineer
Hire when the error is in server actions or route handlers you cannot read, when the fix loop has run three times, or when secrets were pasted into client code to make the build pass. Send the engineer the Vercel build log, the v0 chat link and the GitHub repo if connected. A single fix is €99–$990, about 2 days. See v0 app needs a backend if the missing pieces are server-side.
Top-rated companies for v0 apps
Ranked by our score: published prices, scope of work, AI tools named, timing and a low-risk first step. How we score.
- 1Afterbuild Labs10.0/10Best for: A check before launchFree first step · from $49
- 2Redlab10.0/10Best for: A full rescue by one team that keeps buildingFree first step · from $490
- 3Vibe Code Rescue (Lev Arakelyan)9.0/10Best for: A one-off check and a cleanupFrom $299
Check these
The code lives in a Git repository you own
Connect GitHub or export the project. If the builder account is lost, the product should not be.
Secrets live in the host's environment settings
Keys belong in environment variables on the server, not in the repository or in front-end code.
Dependencies are current and audited
Run npm audit. Critical advisories in packages you ship should be fixed before launch.
No secret keys reach the browser
Open your live app, then DevTools, Sources, and search the loaded JavaScript for sb_secret_, sk_live_, sk-proj- and sk-ant-. Older Supabase keys are long tokens starting with eyJ: decode the middle part of each on your own machine, and if it contains "role":"service_role", your secret key is public. A publishable or anon key in the browser is expected.
Questions
Why did it work in the v0 preview?
The preview does not run the strict production build. Vercel's build type-checks and resolves every import on a clean machine, so hidden errors surface there.
Can I just put the key in the code?
No. Anything in client code or a NEXT_PUBLIC_ variable is shipped to the browser. Server keys belong in Vercel environment variables without that prefix.
Sources: v0: Deployments; Vercel: Troubleshooting build errors; Vercel: How to add environment variables; Next.js: Environment variables.