Nerves won't boot on Raspberry Pi2

I successfully flashed OS onto SD card and inserted card into pi. When I power up the target I see one or two green light flashes and then nothing. The device never shows up on my network.

I am using erlang 26.0.2 and elixir 1.15.4-otp-26. I have set the target to rpi2 to build the firmware.

This is a headless raspbery pi I am using, equipped with a wifi dongle, so I am rather limited in trouble shooting resources. But I wonder if anyone has any suggestions as to how I can get this to work.