Amego offers a highly sophisticated push messaging platform powered by OneSignal (at no additional cost to you).
Using this platform, you can instantly send or schedule push messages that have a title, body, and optional image. These can be sent to all attendees (default) or to a segment that can be as granular as you wish. You can also choose to send messages based on location. Lastly, you can import push notifications if you want to save time.
See full OneSignal Documentation here: https://documentation.onesignal.com/docs/mobile-push-notifications-guide