What are notification channels?
Starting with Android 8.0, apps are required to assign their notifications to so-called “notification channels”. These channels determine which signals (notification sound, light, vibration, etc.) incoming notifications trigger.
For privacy reasons, Threema doesn’t create a separate notification channel for each contact but one for each combination of notification settings. A channel’s ID is a hash of its notification settings.
Editing notification settings
Only edit notification settings for chats and calls in Threema (in Settings > Sound & Notifications or in a chat’s individual notification settings), not in the system preferences. Changes made in the system preferences will be lost.
If you use a Xiaomi device (including Pocophone) running MIUI 10 or later, please enable notification signals as outlined in this guide.