Undefined PHPMailer Function Errors

Problem

While performing an action that causes the system to send an email, you see an Oops! error page that displays the following error:

Call to undefined function PHPMailer\PHPMailer\escapeshellarg() in /path/to/whmcs/vendor/phpmailer/phpmailer/src/PHPMailer.php:1730

You may also see a Required PHP Extensions attention item at Configuration () > System Health.

Cause

The escapeshellarg function is disabled in your server’s PHP configuration.

For more information, see PHP’s escapeshellarg Documentation.

Solution

This troubleshooting information only applies to self-hosted WHMCS installations.

Add the missing extensions to your PHP configuration and then recompile PHP.

troubleshooting troubleshooting-article php-mail oops-errors php

Last modified: 2025 October 17