Welcome to the Community!
If you are using the Netcomm NF7, then it means that the NBN technology you have is FTTP (Fibre to the Premises). For this type of technology, you don't need to set the VLAN ID to 2.
Make sure that your device is running on a 'Router only' mode, then configure the PPPoE with your TPG username and password. Make sure that you have the correct UN and PW by logging in here.
You may use this article as a guide: How to set up TP-LINK C1200 modem for Windows 10
Here's an article that will guide you on how to check the service technology you have. (New Connection Setup Help)
If your third party device can't communicate with the server, then you need to contact the manufacturer to check if you have a faulty device or if they need to make further changes.
You may also check the manual of the device for further assistance on setting it up.
The router will instantly connect on NBN FTTP since it does not require to modify the VLAN ID of the router, but if you wish to use this router to NBN-HFC you have to set up 'VLAN ID 2' to work with TPG NBN.
For additional reference please see this thread Alternate router to use on HFC.
Let us know how it will go and should you require further assistance.
i have just tested with the other premises
it using HFC, i simply connect the router, and it connects with the same account without having to fiddle anything, not even login to the router to change the username to the premises B.
so the router works instantly on HFC, but have trouble with FTTP.
If you are going to use the ASUS RT-AC68U to your NBN FTTB service, then it will not work as it is a router only device.
You have the option to use it as an access point instead.
If you want to use a third party modem/router, you need to make sure that it is a VDSL modem/router in order for it to work with the NBN FTTB technology.
Please be informed that the bundled phone service will not work with a third party device.