Opened the CloudSOC Tenant > Users (upper right corner) > +New > User: Entered User Name, Email, and other required fields and then click Save; found the process failed with an error popup.
"User is already active in ' sample tenant name' account."
The same email cannot be active in two separate tenants because it would cause conflicts with Securlet monitoring and activation (among other potential problems).
There are three options to fix the error.