I have found a solution as to why you can't get remote access through the app on your devices.
Go onto the DVR, right click and go to "System Settings", then go to Network (globe picture), then settings. You'll see at the bottom it will say "Status: Offline".
Tick the box that says Automatic (DHCP) click apply and you should notice that the status will say "Status: Online".
Thats all it took for me to solve the problem, hope this helps others.