Notifications not enabled on my app

I have set up my app to allow for notifications and had previously tested it and it was working. Now, when I or others go into settings on our phones and go to the app, notifications is not even an option. When I go into settings and go to Notifications, the app doesn't even show up in the list. As mentioned, we had previously been able to receive notifications and the Key is set up to do so. Thanks for your help!