Unauthorized: Key Not Found

What This Error Means

The API key stored in WP Mail SMTP doesn’t exist in the Brevo account. Brevo looked up the key and returned “unauthorized: Key not found” because no matching key exists on their end.

Common Causes

• API key was deleted from the Brevo dashboard
• You copied the masked version of an existing key instead of the full key (Brevo masks keys after creation, and the full key cannot be viewed again)
• Typo or extra whitespace when copying the key
• API key belongs to a different Brevo account than the one managing the sending domain

How to Fix

Here is the complete step-by-step guide to resolving the error.

Step 1: Generate a New API Key in Brevo

Log in to your Brevo account and click your organization name in the top-right corner of the page.

Click Settings in the dropdown menu.

After that, click SMTP & API in the left sidebar.

Then click the API keys & MCP tab.

Click the Generate a new API key button (top-right of the page).

Enter a name for the key (e.g., “WP Mail SMTP”) and click Generate.

Copy the API key immediately from the modal. The full key is only shown once. After you close the modal, Brevo masks it, and you can’t retrieve it.

Step 2: Paste the New Key in WP Mail SMTP

Go to WP Mail SMTP » Settings and click the General tab, scroll to the Brevo section, and clear the API Key field.

Then paste the new API key and click Save Settings.

Step 3: Send a Test Email

Go to WP Mail SMTP » Tools. Click the Email Test tab.

Enter a recipient email in the Send To field. Leave the HTML toggle ON.

Once done, click Send Email.

Look for the success message, then check your inbox to confirm the email arrived.

Notes

• Brevo masks API keys after creation. If you see a partially hidden key on the API keys page, do not copy it. Generate a new one instead.
• The full API key starts with xkeysib-. Make sure the value you paste includes the complete string with no extra spaces.
• If the error persists after replacing the key, confirm you are logged into the same Brevo account that owns the sending domain configured in WP Mail SMTP.

That’s It! You now know how to fix the ‘Unauthorized: Key Not Found’ error in Brevo and get your emails sending again through WP Mail SMTP.