Resend idempotency keys in Node: second options arg, one key per email, 24h expiry

TL;DR

A new key defeats the whole mechanism.

Steps

1. A new key defeats the whole mechanism.

When to use

You are seeing this: `js await resend.emails.send( { from: '[SENDER]', to: ['[RECIPIENT]'], subject: 'Welcome', html: '<strong>It works!</strong>', }, { idempotencyKey - 'welcome-user/[USER-ID]', }, ); ` Use this skill when you run into "Resend idempotency keys in Node: second options arg, one key per email, 24h expiry".

When not to use

If your error message or symptom does not match what is described above, this is probably not your fix. Search for your exact error text instead of forcing this one to fit.

Versions

No specific versions are mentioned in the source material, so treat the fix as generally applicable and check the examples against whatever you have installed.

Why this happens

The original report does not dig into a root cause. It documents the symptom and the fix that resolved it.

Resend documents idempotency keys for the send and batch endpoints, with the Node { idempotencyKey } options form, the unique-per-request rule, 24-hour expiry, and the 256-character limit. Verified live at https://resend.com/docs/dashboard/emails/idempotency-keys and https://resend.com/docs/api-reference/emails/send-email.