For a complete article: https://www.blackvoid.club/pushover-notifications-for-all-your-needs/
Configure Pushover with your Synology NAS
To make this work, there are two ways to do it. The reason I will present both is that sometimes, one might not work for you, and the other will. I haven't...
I have a problem with push notifications on my two NAS devices and one VMM. I set push notification to work over Pushover like this:
When I click on the button to get the test message I get it normally. But when there are any other notifications from NAS, I don't get them to...
This setting is turned off by default. Enabling it with mobile push notifications can be useful.
Of course, expect a few false positives (usually when you’re logging in from new places).
While you’re there, check the other options too :)
A simple yet powerful feature that one might miss!
For this to work, you must install Synology's DS Finder on your mobile device (available for iOS and Android).
While you're on your LAN launch DS Finder on your mobile and let it find your DiskStation, login to it and turn on Push notification...