Enabling push notifications for the Hidden iOS app is crucial. Without the ability to send push notifications, Hidden won't be able to track your device.
If you've previously installed Hidden for iOS and didn't enable Push Notifications when initially asked, you will have to go through the following procedure to enable them:
On your phone, open the Settings app, and navigate to Notification Center. Scroll down and find Hidden, make sure the alert style is set to 'Banners', sounds are on (the switch is green), and 'Show on Lock Screen' is on.
Open your Hidden for iOS app and click 'Unregister Device'. Enter your Hidden username and password to complete unregistration.
Once unregistered, click 'Log In' to re-register your device to your control panel.