title: What are the possible reasons to get APNs responses BadDeviceToken or Unregistered?
body: <p>When sending notifications to iOS users, for some of them I get response status code 400 (BadDeviceToken) or code 410 (Unregistered).</p>
  
  <p>From Apple documentation about "BadDeviceToken":</p>
  
  <blockquote>
    <p>The specified device token was bad. Verify that the request contains a valid token and that the token matches the environment.</p>
  </blockquote>
  
  <p>What is the meaning of "bad"? I know for a fact that the device token was valid at some earlier time. What does a user do to make its device token bad? </p>
  
  <p>From documentation about "Unregistered":</p>
  
  <blockquote>
    <p>The device token is inactive for the specified topic.</p>
  </blockquote>
  
  <p>Does this necceserally mean that the app has been deleted? Or there can be some other reasons for this response. </p>