iOS “thread-id” doesn't group push notifications

Question

From the documentation:

thread-id | string | When displaying notifications, the system visually groups notifications with th

Answer 1

Unfortunately, you don't get this for free. You need to create a Notifictation UI extension, and implement your own UI(in this case it's a conversation UI), and update the UI when receive new notification with same thread-id.

Edit: this may not be the correct answer, see a more comprehensive answer here.