I tried manually filling in the fields; it didn't work. Then I tried "Quick Internet Setup" from the GUI, and it still didn't work. The PPPoE login credentials kept going back to the admin login credentials. I even re-installed the settings while amtm was installed, and still, every time I filled in the PPPoE login credentials in the GUI and hit "Apply", they'd go straight back to the router's admin login credentials and fail to connect to the ISP.No way amtm does any of that. Period.
As soon as I uninstalled amtm and restored by settings, everything was back to normal and working fine.