Push Notifications will work with PBXs but they may require some changes in configuration on the PBX.
First, the PBX must be reachable from the public internet. When using push notifications, your SIP Account registers on SIPIS (our server that handles push notifications), instead of from the device. This means that your account must be able to register from the public internet in order for push notifications to work. If your SIP account requires a VPN connection to work, push notifications will not function. If that is the case, you can see our multitasking options at the link below. They should work using the VPN you have configured on the device.
If you would prefer to use different credentials when registering for push notifications, you can. Tap on settings, then SIP Accounts, then your SIP Account. Tap on incoming calls, then push options. Enter the proxy and port you would like to use to register for push notifications and save the change.
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