If notifications don’t work with the @username style (especially for usernames including spaces), you can alternatively use the @userid format. The Slack member ID can be retrieved by first navigating to your Slack profile in the upper left-hand corner of the Slack UI:

  • Click on your profile picture

  • View profile

  • More

  • Copy member ID

Enter this ID prefixed with an @, e.g. @U08CWUG2F into the notification configuration. Notifications should now work.

Slack member ID