Android platform facebook integration

hi I have developed app and integrated Facebook sdk in unity. I invites friends in android platform and notification are successfully going on other android devices. But notification receives only those who has installed Facebook app in their device. They are not getting notification by opening Facebook from the browser. Why it needs app to be installed in device ? Why this thing is happening ?

Please help me thank you

Notification can only be received through FB App not in browser if your register your app as Mobile App in FB developer console.