In very basic terms, once you (or your system) tell us what needs to change, PassKit confirms the Pass is still active (i.e. still in a user's mobile wallet) and then pushes the update to the device, which automatically updates the Pass. If you have selected a notification message, the user will be informed that something has changed in their Pass. A quick swipe of the notification will open the Pass and they will quickly see what has changed.
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