Solid Security Pro has an Inactive Users feature that will send you a notification alerting you when a user hasn't been active in 30 days. This can be very helpful if you have many users and would like to demote or remove the ones that aren't in use. However, depending on the site, you may not want to receive these notifications.
You can add the code below into the wp-config.php file anywhere as long as it is between the first line ( <?php ) and the line that says / That's all, stop editing. Happy Blogging / to disable the notifications. If needed, you can see how to edit the wp-config.php file in this article.