Customer use 'Additional CC email id' to notify the record updates to the recipients other than the submitters. Record notifications are not being sent to the 'CC mail id' users but the submitters are receiving the notificaitons. What could be the issue?

Service Desk Omni channel Notifications
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1

In the email notification rule for the corresponding state ‘CC’ option would not have been checked. Instruct the customer to enable it and then check.