Ensure the Action Center is in Active mode:

1.  Go to Communities > Advocacy
2.  Hover over your Action Center and click Manage Action Center
3.  In the Summary tab click on the Properties sub-tab and look for "Action Center Status" in the center column
4.  If it is in Disabled status click Edit
5. Change the status to Active
6. Click Save

Go back and see if it now shows in the CMS list.