Cursor·FixdeployResendbeginner

Cursor Resend API Key Missing in Production

Quick Answer

How do I fix Cursor Resend API Key Missing in Production?

The Resend API key was added locally but not in the deployed environment, or the backend function is trying to send mail from the browser instead of the server. Start with "Add the Resend key to the deployed environment" before making broader code changes.

Fix signals

What this answers: Why cursor resend api key missing in production happens and what to change first.
Fastest move: Add the Resend key to the deployed environment
Use this page if: Emails work locally but not after deploy

If this keeps happening

Open the next decision, not just the patch

Use these when the current fix is helpful, but the real answer is a better tool choice, a cleaner workflow layer, or a more trustworthy launch path.

Cursor review

Open this when the issue is making you decide whether a more code-first workflow is still the right long-term move.

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Lovable reviews

Open this when the bug is making you reconsider whether a faster generated path would reduce the operational overhead.

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Deploy hub

Open this when the fix is exposing a broader production handoff problem, not just one bug in the code.

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Tool picker

Open this when repeated failures are pushing the decision back up to the stack level.

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Firecrawl review

Open this when the app also needs live web data and the bigger stack question is no longer just about the coding tool.

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Quick Fix Summary

Most likely cause	The Resend API key was added locally but not in the deployed environment, or the backend function is trying to send mail from the browser instead of the server.
Fastest fix	Add the Resend key to the deployed environment
Use this page if	Emails work locally but not after deploy

You're in the right place if...

!Emails work locally but not after deploy
!The form submits, but no email is sent
!Logs show missing RESEND_API_KEY or unauthorized email calls

Why this happens

The Resend API key was added locally but not in the deployed environment, or the backend function is trying to send mail from the browser instead of the server.

Fix

Add the Resend key to the deployed environment

Set RESEND_API_KEY in your deployment platform and redeploy so the server function picks it up.

Make sure email sending happens server-side

Use this prompt to move the mail call out of the frontend if needed.

Copy this prompt

Resend is failing because the API key is missing or being used in the wrong place.
Please move the email send logic to a server-side route or function, read RESEND_API_KEY from server env vars, and return a clear error if the key is missing.

Redeploy and test with a real form submission

After adding the key, submit the form on the live site and confirm the email is sent end to end.

Prevent this next time

Treat every third-party API key as a deployment task. If it sends email, processes payments, or touches data, it belongs in server-side env vars before launch.