Calendar notification - no sound On Xiaomi Redmi Note 4 with MIUI 10, Android 7 there is no way to enable sound for calendar notifications, I get vibrations only. I have tried several calendar apps including Google, MIUI, aCalendar+, various settings including setting battery optimisation off but it never plays a sound, it only vibrates. 

When I press TEST in aCalendar+ notifications settings it vibrates but makes no sound and provides no further help. Of course my sounds are on and I have even tried to turn off bluetooth. I have no SD card, all sounds are stored in internal memory.

Notifications form WhatsApp or Facebook messenger work well with the sound.

Any hints?
Finally figured it out by browsing and reviewing all available settings.

There is an entry Notifications and status bar under System &amp; Devices menu.
There is an entry App notifications and I have enabled everything for aCalendar+ there. Now notifications come with sound finally.

Those settings are quite complicated especially for former Windows Phone users where such stuff worked out of the box.

A good article about the problem is here.