app developer to update their app

I have an app that I need to be able to "Hear" when I get an alert. the notification and sound toggles are switched to on. whenever I receive an alert, it comes in the form of a banner on my homepage. I have to be able to hear the alert when I am asleep or if my phone is in my case. my friend has this exact same app on her android and it has a sound alert. why can't my iPhone have this feature? I need the app developer to update the app to allow for this sound alert. can someone help me with this issue?