Currently the user needs to go to account settings find the mobile push notification option and then register the device.
My suggestion is: just after the user logs in show a banner or maybe a toast notification with a legend saying "do you whant to receive notifications?" and then the button that registers the device.... or something like that
I suggest this because its getting kind of hard explaining users how to do this
thnx ossn team!
Showing a popup it can be added surely a component can be added for you please contact on openteknik.com a component that shows popup if user is from mobile to add device for push notificaiton.

while using the Android app, its inside the account setting menu, in the push mobile notifications, the green button adds and registers the mobile device in order to recieve push notifications.
Where i don't see a option in ossn to receive push notification? if you are using paid version contact openteknik.com
Due to the many requests in the past for additonal features and components we have decided to develope a premium version. Features like Hashtags, Videos, Polls, Events, Stories, Link Preview, etc included in it.
$199 (Life Time)