If you're not receiving push notifications about your visitors arrival and departure, you will need to ensure you have push notifications enabled for the Arke app on your device.
You can check this by going into the 'Settings' of the device, clicking 'Notifications' and then selecting the Arke app.
If you have got notifications for Arke enabled on your device, then it will be a site setting that stops you (and the other residents on your estate) from receiving push notifications on your specific site. In this case, if you would like to receive notifications, please speak to your estate manager and ask them if they can switch the notifications for your site on.