The mail service did not recognise the API key CRM-NG SMTP sent. Copy a fresh key from the provider and paste it into the mailer settings.

This article is for site owners using any API key based mailer, such as Mandrill, SMTP.com, Pepipost, Resend or SendLayer, who see the key being rejected.

What this error means

The service looked up the key that came with the request and found nothing that matches. To the provider, the key does not exist. The message is not about permissions or limits; it is the first check failing.

Common causes

• A character was lost or added while copying, or a space or line break came along with the key.
• The key was revoked, deleted or regenerated in the provider's dashboard.
• The key belongs to a different product of the same company. For example, a Mailchimp marketing key does not work for Mandrill; Mandrill keys are created in the Mandrill app.
• A test-mode or sandbox key was used where a live key is required.
• The key was set in wp-config.php with a CRMNG_SMTP_* constant that still holds an old value.
• The site was restored from a backup or cloned, and the encrypted key could not be read with the current encryption key.

How to fix

1. Open the provider's key page

   Mandrill: Settings → SMTP & API Info. SMTP.com: the API keys page in your account settings. Pepipost (Netcore): the integrations or API settings page. Resend: API Keys. SendLayer: Settings → API Keys.

2. Create a new key

   Make a new key for this site and copy it once, in full, without spaces.

3. Replace the stored key

   Go to CRM-NG SMTP → Settings → General, confirm the Mailer is the right service, press Remove API Key, and paste the new key into API Key. For SMTP.com also check Sender Name matches a sender in your account.

4. Save

   Wait for "Settings were successfully saved."

5. Send a test

   Go to CRM-NG SMTP → Tools → Email Test, fill in Send To and press Send Email.

Verify it worked

The test page shows "Test email sent successfully! Check your inbox to confirm delivery." The provider's activity page lists the message.

Notes

• If the API Key field is greyed out, change the constant in wp-config.php. See secure settings with constants.
• After moving a site, CRM-NG SMTP may not be able to decrypt secrets saved on the old site if the encryption key changed. Re-enter the key, or set CRMNG_SMTP_CRYPTO_KEY to the same value on both sites.
• SendGrid and Brevo have their own articles for their key errors. See the related links.
• Store keys only in CRM-NG SMTP or wp-config.php. Never send them by email or chat; see sharing credentials safely.

Related

• Mandrill mailer guide
• SMTP.com mailer guide
• Pepipost mailer guide
• Resend mailer guide
• SendLayer mailer guide
• Error: Authorization grant invalid or expired (SendGrid)
• Error: Unauthorized: key not found (Brevo)
• Troubleshooting email delivery