It sounds like you may have added the camera to the app using the "online device" option, which adds the camera using its local IP address. The result would be that the camera is only accessible when your on the same local network but not via the Internet.
Before trying an alternative method it might be best to delete the camera from your app and reset it first.
The best process for setting the camera up for remote access is to login to ProControl+ and select "Add device". This should open your phones camera which you use to scan the QR (square barcode) code on the back of the camera. You then proceed to enter your WiFi details, select the device type (wireless camera in this case) and hopefully it will successfully connect to your network. Once connected using this method the camera should be accessible both at home and when away.
The success of this method depends on your phone being connected to the same WiFi as the camera (not an extender) during the set-up and the WiFi being a 2.4 GHz connection.
If you have a dual band router and both frequencies are combined into one you may need to disable the 5 GHz or create a guest network that only uses 2.4 GHz and use that.