You are getting a notification email from Symantec Endpoint Protection Manager (SEPM) about the paid/trial license which is expired.
You want to delete the expired license from SEPM.
The notification is enabled by default, reference: How do I receive a notification that my Symantec Endpoint Protection licenses are expiring?
LiveUpdate will also fail in case of expired license and a Notification is created, send on email.
A paid/trial SEP license has expired and it is not been removed from the SEPM.
Follow the instructions below to delete the expired license(es).
Note: If only the Trial License present under Licenses, it cannot be removed as the Delete License option will not be available under Tasks.
In this scenario, you may disable the notification or remove the email address to stop receiving the emails.