### [Error: API Key Invalid](https://wpmailsmtp.com/docs/smtpcom-api-key-invalid/)

**Published:** May 18, 2026
**Author:** David Ozokoye

**Content:**

**Note**: This guide applies to the [SMTP.com mailer](https://wpmailsmtp.com/docs/how-to-set-up-the-smtp-com-mailer-in-wp-mail-smtp/ "SMTP.com") in WP Mail SMTP.

## What This Error Means

The API key stored in WP Mail SMTP doesn’t match any active API key in the SMTP.com account. SMTP.com rejects the request before WP Mail SMTP can send any email.

## Common Causes

- You deleted or regenerated the API key in the SMTP.com dashboard without updating WP Mail SMTP
- Wrong key copied (partial key, or key from a different account)
- The pasted key includes leading or trailing whitespace
- SMTP.com suspended the account, invalidating all keys

## How to Fix

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

### Step 1: Copy the API Key from SMTP.com

The API key is always visible on the SMTP.com settings page, so re-copying it is the fastest fix.

Start by logging in to your [SMTP.com](https://my.smtp.com/ "SMTP.com") account. Then, go to **Account » My Settings** and click the **API** tab.

Finally, find the API key in the **Key** column and copy the full value.

![API key in the Key column on the API tab](https://wpmailsmtp.com/wp-content/uploads/2026/05/smtp-api-key-2.png)**Note**: SMTP.com API keys are long alphanumeric strings. Use copy and paste to avoid truncation or typos, and make sure there are no leading or trailing spaces.

### Step 2: Paste the Key in WP Mail SMTP

With the new API key copied, update the value in WP Mail SMTP.

Start by going to **WP Mail SMTP » Settings** and clicking the **General** tab. Then, scroll to the **SMTP.com** section and paste the key into the **API Key** field.

![Paste the API key into the API Key field in WP Mail SMTP](https://wpmailsmtp.com/wp-content/uploads/2026/05/get-api-key-link-2.png)Finally, click **Save Settings**.

### Step 3: Send a Test Email

Confirm the fix by sending a test email.

To test the fix, go to **WP Mail SMTP » Tools** and click the **Email Test** tab. Enter a recipient address in the **Send To** field, leave the **HTML** toggle ON, and click **Send Email**.

![Test email tab](https://wpmailsmtp.com/wp-content/uploads/2024/10/test-email-tab-1024x1002.png)Once done, check for a success message and confirm the email arrived in the recipient inbox.

## Notes

- SMTP.com API keys are long alphanumeric strings. Use copy and paste to avoid truncation or typos, and make sure there are no leading or trailing spaces.
- If the SMTP.com account was suspended, contact SMTP.com support to resolve the suspension before copying the key. A valid key won’t work on a suspended account.

That’s It! You now know how to fix the ‘API Key Invalid’ error in SMTP.com and get your emails sending again through WP Mail SMTP.

**Categories:** SMTP.com Errors, Error Library

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