PPPoE Connection (with VLAN Tag) - Dynamic DNS returns "noconnect" on pppoe, no IP address for other

I have a EdgeRouter, and I used the "Basic Setup" wizard to configure a PPPoE connection on eth0.

I'm trying to setup a Dynamic DNS service using DynDNS, via the GUI. This is the output:

ubnt@ubnt# show service dns dynamic
 interface eth0 {
     service dyndns {
         host-name SANITISED.dyndns.org
         login victorhooi
         password SANITISED
     }
     web dyndns
 }
[edit]

However, no matter what interface I set it to, it doesn't seem to work.

If I set it to pppoe (which according to the dashboard is the interface with a public IP address), I get:

ubnt@ubnt:~$ show dns dynamic status
interface    : pppoe0
host-name    : cco.dyndns.org
last update  : Thu Jan  1 10:00:00 1970
update-status: noconnect

If I set it to eth0, I get:

ubnt@ubnt:~$ show dns dynamic status
interface    : eth0 [ Currently no IP address ]

If I set it to eth0.0 (not sure what this is - I believe it's related to my VLAN 0 on eth0?):

ubnt@ubnt:~$ show dns dynamic status
interface    : eth0.0 [ Currently no IP address ]

This is the output of show interfaces (public IP sanitised):

ubnt@ubnt:~$ show interfaces
Codes: S - State, L - Link, u - Up, D - Down, A - Admin Down
Interface    IP Address                        S/L  Description
---------    ----------                        ---  -----------
eth0         -                                 u/u
eth0.0       -                                 u/u  Internet (PPPoE)
eth1         192.168.1.1/24                    u/D  Local
eth2         -                                 u/D  Local 2
eth3         -                                 u/u  Local 2
eth4         -                                 u/u  Local 2
lo           127.0.0.1/8                       u/u
             ::1/128
pppoe0       120.150.SAN.SAN                   u/u
switch0      192.168.2.1/24                    u/u  Local 2

Any thoughts on how to get this working?