Based on the screenshot that you've sent, I've noticed something wrong.
-Does your internet connection require a login? Should be (YES).
-It should ask for your PPP username and password (which pertains to your TPG username and password)
Save the changes, then check if it's going to connect. Make sure that the router is connected directly to the NBN NTD.
If the device is still not authenticating to the server, then contact Netgear support for further assistance.
As in these settings:
VLAN ID on WAN is set to 2.
On top of the VLAN tagging, here are the other settings you need:
Connection Type = PPPoE
PPPoE Username = TPG username
PPPoE Password = TPG Password