You can set default settings for users at https://app.bigtincan.com/admin/users
Click on the pencil icon next to All Users and select User Default Settings
The settings available are what default values can be set for a newly created user. Check the Update Existing Users box to update existing users who have already been created
Click on the pencil icon next to All Users and select User Default Notifications.
Be sure to check the column Update All Users to change the settings for users already created in the Hub.
Ensure that allow notifications are checked for the story that you have published