TL;DR

Go to Beeper Android → Settings → Notifications → Configure Noisy/Default Notifications → Enable "Pop on screen"

How to enable Pop on screen notifications on Beeper Android?

While using Beeper Android, you should be able to receive “Pop on screen” notifications but is for some reason you don't see them on your device, follow these steps to enable this feature.

1. Open the Beeper Android app.
2. Tap the top right gear menu → Settings
3. Tap Notifications
4. Tap Configure Noisy/Default Notifications
5. Toggle "Pop on screen" on. (If it was already enabled, toggle it off and on again)