I can answer my own question. No quick response from TP, so I paid a Tech, and he fixed it instantly. At the setup screen for IPs, there are three options: static, dynamic and PPPoE, with the comment...

Just bought a 3 disc M5 Deco mesh system. Setup finds the deco OK, then connects to the internet (i.e.if I plug a cable into the second port on the Deco, I get internet) In the final stages of setup,...