At some events, People also lists people who registered but have not opened the app yet. Select Notify me when they join on their card to get a push notification when they join.
Where to find it
People (or the name your organizer gave it) > Attendees: cards that say "<first name> hasn't joined the app yet." have a Notify me when they join button.
The same button is at the bottom of the person's profile.
The mobile app and the web app work the same way.
Ask to be notified
Open People > Attendees and find the person.
Select Notify me when they join.
If notifications are off, the app asks you to turn them on first. Select Enable notifications and allow them in the prompt from your phone or browser. The request is saved once notifications are on.
The app confirms: "You'll get a push notification when <first name> joins the event." The button changes to Cancel notification.
To stop, select Cancel notification. The app shows "Notification canceled".
When the person joins
Brella sends the notification when the person joins with the invitation sent to their registration email.
You get a push notification with the event name as the title and "<name> just joined the event." as the message. Select it to open their profile.
Activity on the Home screen gets an entry with the text "You can now connect with them!". Select it to open their profile.
The person stays in your Bookmarks, so you can find them later and send a meeting request or start a chat.
Good to know
You can't chat with or send a meeting request to someone who has not joined yet. The button is the only action on their card.
People you asked about appear in People > Bookmarks before they join.
The notification is a push notification. If no device of yours is registered for notifications when the person joins, you get no alert and no Activity entry, but the person still stays in your Bookmarks.
If you don't see anyone marked "hasn't joined the app yet", the organizer has turned this off, or everyone has joined.
Some branded event apps do not show who has joined. In those apps the card says "<first name> is not available for networking." and there is no button.
Troubleshooting
The app keeps asking you to turn on notifications
The request is saved only after notifications are on. Open Account > Notifications and turn them on, then select the button again. See Get event announcements for the browser and phone settings.
You were not notified, but the person has joined
The person joined without their invitation, for example with a different email than the one on their registration. The app treats them as a new attendee. Search for them in People > Attendees.