Open the full Vercel deployment log

In Lovable, click the deploy that failed. There is usually a 'View build logs' or 'Open in Vercel' link at the bottom. Open it. The Vercel log shows the actual stack trace, which is what you need. If you cannot find the link, go to vercel.com, find the project Lovable created (it has your slug), and look at the last failed deployment.

Check for missing environment variables in production

Lovable's editor uses development env vars by default. Your deploy uses production env vars. If you added a new env var (Stripe key, Supabase URL, API token) and only set it for development, the deploy will fail or run with the wrong values. In the Lovable project settings, go to Environment Variables and make sure every variable has a Production value.

Look for TypeScript errors the editor was suppressing

Lovable's editor often has 'noEmitOnError: false' which means TypeScript errors do not block the dev server. The Vercel production build does check types. Look in the build log for lines starting with 'Type error:' and fix them. The most common ones are unused imports, missing return types on async functions, or any/unknown mismatches.

Verify all Supabase migrations have actually run

If your code references a table or column that exists in your migrations but was never run against your production Supabase project, the build technically succeeds but the runtime crashes immediately. In the Supabase dashboard, go to Database then Migrations. Make sure the latest migration timestamp matches what is in your Lovable repo.

Search the codebase for localhost references

Lovable AI sometimes hardcodes http://localhost:3000 in fetch calls or redirect URLs. These work in the editor and fail in production. Search the codebase for 'localhost' and replace with relative paths or the production URL.

Lovable

How to Fix Lovable Deployment Failures and Build Errors

Your Lovable app builds fine in the editor but fails to deploy. The four most common causes and exactly how to fix each one.

TL;DR

Lovable deploy failures usually come down to: stale environment variables, an unresolved TypeScript error the editor was hiding, a Supabase migration that never actually ran, or a hardcoded localhost reference. Check them in that order.

What is actually happening

Lovable's deploy step bundles your app and pushes it to a hosted Vercel deployment. The editor uses a more permissive build, so code that runs locally can fail in the production build. The deploy logs are usually truncated in the Lovable UI, which makes the actual error hard to find.

The fix, in order

Try these in sequence. Most apps are fixed by the first or second step.

1
Open the full Vercel deployment log
In Lovable, click the deploy that failed. There is usually a 'View build logs' or 'Open in Vercel' link at the bottom. Open it. The Vercel log shows the actual stack trace, which is what you need. If you cannot find the link, go to vercel.com, find the project Lovable created (it has your slug), and look at the last failed deployment.
2
Check for missing environment variables in production
Lovable's editor uses development env vars by default. Your deploy uses production env vars. If you added a new env var (Stripe key, Supabase URL, API token) and only set it for development, the deploy will fail or run with the wrong values. In the Lovable project settings, go to Environment Variables and make sure every variable has a Production value.
3
Look for TypeScript errors the editor was suppressing
Lovable's editor often has 'noEmitOnError: false' which means TypeScript errors do not block the dev server. The Vercel production build does check types. Look in the build log for lines starting with 'Type error:' and fix them. The most common ones are unused imports, missing return types on async functions, or any/unknown mismatches.
4
Verify all Supabase migrations have actually run
If your code references a table or column that exists in your migrations but was never run against your production Supabase project, the build technically succeeds but the runtime crashes immediately. In the Supabase dashboard, go to Database then Migrations. Make sure the latest migration timestamp matches what is in your Lovable repo.
5
Search the codebase for localhost references
Lovable AI sometimes hardcodes http://localhost:3000 in fetch calls or redirect URLs. These work in the editor and fail in production. Search the codebase for 'localhost' and replace with relative paths or the production URL.

When to stop debugging and get help

If the build log shows a clear error you can fix, you do not need help. If the log shows something cryptic like 'Module not found' or 'Cannot find module after build' and standard fixes do not work, the project structure itself is probably broken in a way that needs a real engineer.

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