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ERR-123

Lovable Preview Works, Production Broken? 3 Fixes (2026)

Lovable Preview Works, Production Broken? 3 Fixes (2026)

Last updated 15 April 2026 · 8 min read · By Hyder Shah

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Direct answer

Your Lovable app almost always breaks in production for one of three reasons: missing environment variables, Supabase Row-Level Security that wasn’t enabled, or a Google OAuth redirect URL still pointing at localhost. Check them in that order — 85% of broken Lovable apps we rescue fail on one of these three.

Quick fix for Lovable Preview Works, Production Broken

Start here

Fix 1 — Missing environment variables (55% of cases)

In Lovable, open Settings → Environment Variables. List every key your preview uses. Common ones: VITE_SUPABASE_URL, VITE_SUPABASE_ANON_KEY, STRIPE_PUBLISHABLE_KEY, RESEND_API_KEY.

On your production host (Vercel, Netlify, Fly), add every variable with productionvalues — not preview values. Redeploy. Hard-refresh.

If you still see a blank page: check the production build log for undefinedreferences. That’s always a missing env var.

Deeper fixes when the quick fix fails

02
Fix 2 — Supabase Row-Level Security wasn't enabled (30% of cases)
This is the failure captured by the widely-reported February 2026 Lovable/Supabase RLS disclosure — RLS is off by default in Lovable’s preview.
In Supabase, go to Authentication → Policies. For every table, confirm RLS shows Enabled (green). If off, enable it and add minimum policies:
```
create policy "Users see own rows"
  on public.your_table
  for select
  using (auth.uid() = user_id);
```
Test with two users in incognito windows. They should not see each other’s rows. If RLS has been off since launch, assume bots have scraped your data — rotate the anon key and notify users.
03
Fix 3 — OAuth redirect pointing at localhost (15% of cases)
In Supabase, go to Authentication → URL Configuration. Set Site URL to your production domain. Under Redirect URLs, add every legitimate variant like https://yourapp.com/** and https://yourapp.com/auth/callback.
In Google Cloud Console → Credentials → OAuth 2.0 Client, add the production domain to Authorized redirect URIs. Redeploy. Test in an incognito window.

Still broken after all three?

You’re in the rarer 15%. Usually one of:

CORS failure on a custom API — check Supabase Edge Function CORS headers.
Type mismatch between preview and prod — run tsc --noEmit locally.
Build caching on the host — purge Vercel/Netlify cache and redeploy.

Why AI-built apps hit Lovable Preview Works, Production Broken

Lovable’s preview environment is a managed sandbox — it silently fills in things your real production host won’t: a working database URL, auto-wired auth callbacks, and permissive default security. The instant you publish to a custom domain or export to GitHub, those crutches disappear. Users don’t notice until the first real login fails.

It also isn’t a one-off Lovable quirk: industry benchmarks put AI-code vulnerability rates close to half (see our 2026 research), and RLS misconfiguration is the single most common class on Supabase-backed apps.

“The login screen, which had been fine, suddenly started throwing an error I didn't understand.”

Nadia Okafor, Vibe Coding in 2026 (Medium)[source]

Diagnose Lovable Preview Works, Production Broken by failure mode

Open your deployed app and check the browser console (right-click → Inspect → Console). The error pattern tells you which of the three you’re hitting.

Error pattern	Root cause	Fix
supabaseUrl is required, or blank page	Missing env vars	Fix #1
Login succeeds but user sees other people's data, or empty data	RLS disabled	Fix #2
Login redirects to localhost:3000 then 404s	OAuth redirect misconfigured	Fix #3
Network tab shows 500 from /api/*	Usually env vars; occasionally RLS	Fix #1, then #2

Related errors we fix

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Lovable Preview Works, Production Broken questions

Why does Lovable preview work but production breaks?+

Lovable preview uses a managed sandbox that auto-wires environment variables, permissive security, and auth callbacks. Production doesn't. The moment you publish to a real domain, you have to configure those three things yourself. 85% of broken production Lovable apps fail on environment variables, Row-Level Security, or OAuth redirect URLs — in that order.

How do I check if Supabase RLS is enabled on my Lovable app?+

Open your Supabase project dashboard, go to Authentication → Policies, and check every table. Each table must show RLS as Enabled. If any table is disabled, log in as two different users in incognito windows — if one sees the other's data, you have a live security hole.

Can I fix a broken Lovable deployment myself?+

Yes, 85% of the time. The three most common causes (env vars, RLS, OAuth redirects) each take 5–15 minutes to fix. If none of the three apply, the remaining causes (CORS, TypeScript mismatches, build cache) are harder and often signal deeper architectural issues.

How much does it cost to hire someone to fix a broken Lovable app?+

Fixed-price Lovable rescue typically runs $299 for single-bug Emergency Triage, $1,999 for a full Deploy-to-Production pass, or $7,499 for finishing an entire MVP. Hourly freelance rates run $50–$150/hour on Upwork; expect 5–40 hours depending on severity.

Is Lovable safe for production?+

Lovable can be made production-safe, but it is not safe by default. Research shows roughly 70% of Lovable-built apps ship with Supabase Row-Level Security disabled, and industry benchmarks put AI-code vulnerability rates close to half (see our 2026 research). A security audit before launch is mandatory.

What breaks most often when you deploy a Lovable app?+

In order: (1) environment variables not propagated to production, (2) Row-Level Security left disabled in Supabase, (3) OAuth redirect URLs pointing at localhost, (4) Custom-domain SSL not provisioned, (5) Stripe webhooks pointing at the preview URL. Those five account for over 90% of deployment failures.

Next step

Ship the fix. Keep the fix.

Emergency Triage restores service in 48 hours. Break the Fix Loop rebuilds CI so this error cannot ship again.

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About the author

Hyder Shah leads Afterbuild Labs, shipping production rescues for apps built in Lovable, Bolt.new, Cursor, Replit, v0, and Base44. our rescue methodology.

Lovable Preview Works, Production Broken experts

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