This is a solution if you set an MP3 file or other file on your device as your alarm sound, but the default alarm sound actually plays.
This method is possible with ver.20 or higher. If you cannot find the item, please update the app.
1. Open Settings on your device.

2. Settings → Apps → Reminder FLEX → Permission →Music & Audio and set “Allow”





And check if your selected music is ring for the alarm or not.