I think the confusion is coming with the terminology used here.
When you're at home, you can access things on your home network using local IP addresses. When you leave, you have to use the external (internet) IP address and the port, with port forwarding setup in your router/home network, which (in those settings) will point to your local IP for your scanner.
Don't enter it here but to verify, you're entering your external IP address, a colon, and the port when you're on the cellular network (not our home wifi) correct?
When you're at home, you can access things on your home network using local IP addresses. When you leave, you have to use the external (internet) IP address and the port, with port forwarding setup in your router/home network, which (in those settings) will point to your local IP for your scanner.
Don't enter it here but to verify, you're entering your external IP address, a colon, and the port when you're on the cellular network (not our home wifi) correct?