How to get PPPD to work with systemd-networkd?

This appears similar to another question , but nothing was ever followed up on it. I'm currently having trouble with pppd as a systemd service. I'm waiting for the network adapter to come online before attempting to setup the pppoe link. The service:

[Unit]
Description=PPPoE connection
After=network.target

[Service]
Type=oneshot
ExecStart=/usr/sbin/pppd call dsl-provider
Restart=on-failure

[Install]
WantedBy=sys-subsystem-net-devices-eth1.device

Where eth1 is the device upon which the pppoe link will be made. Inspection of the service's logs with journalctl -u pppoe.service shows:

debian systemd[1] : Starting pppoe.service - PPPoE connection...
debian pppd: Plugin rp-pppoe.so loaded.
debian pppd: Plugin rp-pppoe.so loaded.
debian pppd: pppd 2.4.9 started by root, uid 0
debian pppd: Timeout waiting for PADO packets
debian pppd: Unable to complete PPPoE Discovery
...
debian pppd: Timeout waiting for PADO packets
debian pppd: Unable to complete PPPoE Discovery
debian pppd: Exit.
debian systemd[1] : pppoe.service: Deactivated successfully.
debian systemd[1] : Finished pppoe.service - PPPoE connection.

This is the same whether the service is run automatically at boot or with systemctl start pppoe. When pppd is run manually with pppd call dsl-provider it works as expected. What could be causing this issue? Thanks