Unable to update plugins and/or themes requiring a license for automatic updates in WP Toolkit in Plesk

Symptoms

It is not possible to update custom (paid) plugins and/or themes in Plesk in WordPress > example.com > Updates, with the following warning:

PLESK_WARN: Selected items were updated with errors:
-Unable to update plugin 'all-in-one-seo-pack-pro_3.3.4_2', details: One of the common causes of this error is plugin or theme requiring a license to be updated. Log in to WordPress admin dashboard and try updating this plugin or theme there to discover more details about the issue.

Cause

License required for the plugin/theme updates.

WordPress Toolkit can update paid plugins & themes if these updates are available in the WordPress admin area.
However, plugins and themes that require a license for automatic update will cause the above warning message to show when trying to update them via WordPress Toolkit without a license.

Resolution

Install and activate the corresponding license for the plugin and/or theme to allow automatic updates.