There are several things that need to be in place for Group notifications to work.
Are you signed into the myParish app with the same account that you joined the group with?
Do you have notifications turned on within the phone settings for the myParish app?
Do you have notifications turned on for the specific group within the myParish app “My Account” tab?
Is your phone’s operating system up to date? Check your phone settings for operating system updates.
Is the myParish app up to date? Check your app store for updates.
Do you have a strong internet connection? Check WiFi and Data.