When the VMP Server wants to send a message or other notification to a device running Vocera Collaboration Suite on the iOS operating system and the device is not on the corporate network, it sends the notification to the Apple Push Notification Service (APNS), which then sends the notification to the device.
The connection to the APNS uses a security certificate, which is included as part of the VMP Server installation process. This certificate needs to be updated every year. The Vocera support team will contact you when your APNS certificate is about to expire.
After you have received your updated certificate file, you can use the VMP Enterprise Manager to update the VMP Server to use the new certificate.