@TP-Link after lots of troubleshooting with IINET, we solved the problem. This may happen to others so it's important to inform, on the setup app there is a additional button below the internet setup...

Just bought the deco X 20 mesh system. Trying to set it up to the NBN modem, I get all the way through the App set up and at the end the LED goes solid red. No idea what is going on! Please help