First, please update your phone to the latest iOS version, and the app to the latest version from the App Store.
Then, In the Times tab, make sure you have selected the sounds you want for each prayer.
Also, make sure you have allowed notifications in iOS Settings. In the app, go to Settings > System > iOS Settings > Notifications > Allow Notifications.
Then you can test the notifications by going back into the app > Settings > Scheduled reminders > swipe left on any notification > tap Test. That will allow you to see if the notifications are working (visual and audio)