How to support push notification in safari on a flutter webapp

Question

I have a flutter project which is running on iOS, Android and Web.

Now my challenge is to support push notification in Safari browser (webapp flutter). I should be able to send custom payload in push notification.

I have gone though the below official documentation, but not getting how to pass custom payload with this approach and also there is NO CALLBACK defined to handle the push notification

https://developer.apple.com/library/archive/documentation/NetworkingInternet/Conceptual/NotificationProgrammingGuideForWebsites/PushNotifications/PushNotifications.html

Please help me out.