title: What is the difference between VoIP notifications and notification sent with apns-priority 10?
body: <p>Here's what <a href="https://developer.apple.com/library/content/documentation/NetworkingInternet/Conceptual/RemoteNotificationsPG/CommunicatingwithAPNs.html#//apple_ref/doc/uid/TP40008194-CH11-SW1" rel="noreferrer">docs</a> state:</p>
  
  <blockquote>
    <p>The priority of the notification. Specify one of the following values:</p>
    
    <p>10–Send the push message immediately. Notifications with this priority
    must trigger an alert, sound, or badge on the target device. It is an
    error to use this priority for a push notification that contains only
    the <code>content-available</code> key.</p>
    
    <p>5—Send the push message at a time that takes into account power
    considerations for the device. Notifications with this priority might
    be grouped and delivered in bursts. They are throttled, and in some
    cases are not delivered.</p>
  </blockquote>
  
  <p>And about <a href="https://developer.apple.com/library/content/documentation/Performance/Conceptual/EnergyGuide-iOS/OptimizeVoIP.html" rel="noreferrer">VoIP</a>:</p>
  
  <blockquote>
    <p>Instead of persistent connections, developers should use the PushKit
    framework—APIs that allows an app to receive pushes (notifications
    when data is available) from a remote server. Whenever a push is
    received, the app is called to action. For example, a VoIP app could
    display an alert when a call is received, and provide an option to
    accept or reject the call. It could even begin taking precursory steps
    to initiate the call, in the event the user decides to accept.</p>
  </blockquote>
  
  <p>Do I understand correctly that <code>apns-priority</code> defines message queuing at APNS side, and VoIP push type defines what happens on the device?</p>
  
  <p>And what do they mean saying </p>
  
  <blockquote>
    <p>It is an error to use this priority for a push notification that contains only the <code>content-available</code> key.</p>
  </blockquote>
  
  <p>Will APNS return an error or is it just a bad practice?</p>
  
  <p>P.S. I use AWS SNS for sending notifications and it does not support customisation of <code>apns-priority</code>, but I am curious how it affects the process.</p>