1. Check that your phone is not in power saving mode, Do Not Disturb mode, or any other focus mode.
2. Prevent the app from being stopped in the background. Enable auto-start.
3. Verify that notifications are enabled both in the system settings and in the DuoxMe app.
4. Check that lock screen notifications are enabled.
5. Make sure the DuoxMe application always has an internet connection (that is, that data usage restriction is not enabled). Enable Stay connected when the device is in sleep mode.
6. Disable Battery Optimization for DuoxMe.