Unable to connect my NETGEAR ORBI RBK13 WIRELESS AC1200 MESH ROUTER to Foxtel NBN modem.

This is very helpful, thanks.

This is a combination modem/router/WiFi device.  It is intended to provide the Foxtel customer with a complete home networking solution, similar to the Netgear Orbi.

There are two ways to integrate the Orbi RBK13 system:

1. Unplug that ethernet cable with the red connector from the FoxTel and connect it to the RBK10 WAN port.
   In essence, do not use the FoxTel device at all.
   Let it sit in a box somewhere in case the Orbi fails or to return when (if?) you terminate the FoxTel service and they want it back.
   This has the benefit of having only one router and only one WiFi network in the house.
2. Use an ethernet cable to connect the Orbi WAN port to one of the Foxtel's yellow ethernet ports.
   Once the Orbi is connected, in about three minutes it should begin broadcasting the WiFi name (SSID) that is printed on the product label and devices can connect to it using the password printed on the label.
   This will result in having two routers (Foxtel and Orbi), two ethernet networks, and two WiFi networks in the house, which has the potential to cause problems in the future. https://kb.netgear.com/30186/What-is-Double-NAT 
   If any of these potential issues apply to you, then there are ways to turn one of the devices into "not a router".