I am not getting any notification and when i am sending invite to a friend so there i am getting error that "No push subscription available for receiver."

[Aman-moondive]

receiver Push Subscription: []
No push subscription available for receiver.

And what is the Vvid for sending Notification and we can use any alternate for that and what is the send in the notification like link of the call or call notification like in instagram or whatsapp.