Lucid Dream function doesn't work

If i go in settings to lucid dreaming and press preview nothing happenes. If i enable vibrations i only hear the vibrations. It shows on the graph that it played the sound. I can’t really know if it played the audio cue as i was sleeping. I tried it on the phone of a friend and the preview actually worked.
I have a Xiaomi Redmi Note 4X and the latest version of Sleep as Android.

Edit: I got it to work somehow but it’s extremely quiet even at 100 % volume. I can barely hear it when i’m awake. I doubt i will be able to hear it while sleeping

Edit 2: I realised why i wasn’t hearing anything. It doesn’t work on Silent mode.

Edit 3(probably last) : It looks like the Lucid Dreaming function volume is influenced by notification volume and not general volume.