Android
Go to Plusgram/Telegram settings notifications and sounds, make sure notifications are turned on and importance is set to high or higher.
Check if the contact or group is muted.
Make sure you have Google Play Services installed on your phone.
Check Plusgram/Telegram notification priority in Android settings, depending on your device it can be called importance or behavior.
If your phone uses some battery saving software, please make sure Plusgram/Telegram is whitelisted in the app.
Note: Huawei and Xiaomi devices have evil task killer services that interfere with Plusgram/Telegram notification services. In order for our notifications to work, you need to add Plusgram/Telegram to the allowed apps in the security settings of these devices. Huawei : Phone Manager App > Protected Apps > Add Plusgram/Telegram to the list. Xiaomi: Services > Security > Permissions > Auto-start, find Plusgram/Telegram and enable auto-start.