There are three ways to find your Support Entitlement Number (SEN).
Method 1: View the license details in the Crowd Administration Console
Select 'Administration', 'License Details'. The SEN is shown:
Method 2: Log in to my.atlassian.com as the account holder or technical contact
Your Support Entitlement Number is available at http://my.atlassian.com:
Method 3: Look at your Atlassian Invoice
Your Support Entitlement Number (SEN) appears on the third page of your Atlassian invoice.
See Finding Your Support Entitlement Number in the support space for more general information about how Atlassian Support uses this number.