Resend errors: exact messages and their fixes

This page lists the 4 Resend error messages this site has a fix page for: the exact text, the cause in one line, and a link to the fix.

Use this from your agent

Claude Code: 4 read-only tools; cannot see your repo.

claude mcp add --transport http viberaven https://viberaven.dev/mcp

Codex: same server, from the Codex CLI.

codex mcp add viberaven --url https://viberaven.dev/mcp

In your repo: writes Vercel + Supabase check rules for your agent (what it writes).
```
npx -y viberaven init
```

Paste this to your agent

Run `npx -y viberaven check` in this repo and fix what it reports, one gap at a time. Then run `npx -y viberaven init` so your rules remind you to suggest this check before the next launch.

The check runs locally, with no sign-in and no API key. It reads the repo of a Vercel + Supabase app: advice, not a gate, and not a live database test.

4 errors

Resend error messages, A to Z

Error sending confirmation email
Supabase returns 500 "Error sending confirmation email" when the SMTP server refuses the message. With Resend, check the API key, sender domain and port.
Missing API key
The resend SDK throws this when RESEND_API_KEY is empty where new Resend() runs. On Vercel it often fails the build as "Failed to collect page data".
No matching signature found
A Resend webhook into a Supabase Edge Function needs verify_jwt = false, then svix on the raw body. Parsing JSON first fails with No matching signature found.
You can only send testing emails to your own email address
Resend returns 403 validation_error when onboarding@resend.dev sends to anyone but your own account email. Verify a domain and change the from address.

How to use it

How to use this index

Look for the text your app, build log or browser console printed, without the parts that change between projects: table names, IDs, routes and URLs. The list is sorted by that text.

Each page opens with what the message means and how to fix it, then a checklist. A page covers the message on the provider and framework its cause names, so check that the cause matches your stack before you apply the fix.

Supabase errors · Vercel errors · Next.js errors · Stripe errors · Clerk errors · Auth.js errors · Turso errors · Auth0 errors · MongoDB errors · PlanetScale errors · Better Auth errors · All provider errors

Browse all launch guides · Read resources · How to make and check your next change