Trying this out on 16.1 Beta. I get a 200 (Success) from APNS but never see the state of the LiveActivity change.
Confirmed that I was using the pushToken obtained after starting activity.
Also, looking at the fields in APS payload, how does it identify which LiveActivity to update. When using client side APIs, code can pick the activity to update. But with APS, there doesn't seem to be a way.
UPDATE:
Works now. I was manually creating the aps payload and not updating the timestamp.