What are the possible reasons to get APNs responses BadDeviceToken or Unregistered?

Question

When sending notifications to iOS users, for some of them I get response status code 400 (BadDeviceToken) or code 410 (Unregistered).

From Apple documentation about \"Ba

Answer 1

I was sending a "development" device token to the "production" apple push servers. I fixed it by sending requests to api.development.push.apple.com instead of api.push.apple.com