Using ImageBuilder for olinuxino-maxi

I'm trying to build an image for the Olimex iMX233-OLinuXino-MAXI using the ImageBuilder. I've tried both the 18.06.5 and the 19.07.0-rc1 ImageBuilders and I get the same error on both:

Configuring ppp-mod-pppoe.
Collected errors:
 * opkg_install_cmd: Cannot install package imx-bootlets.
 * opkg_install_cmd: Cannot install package uboot-mxs-mx23_olinuxino.
Makefile:149: recipe for target 'package_install' failed
make[2]: *** [package_install] Error 255
Makefile:108: recipe for target '_call_image' failed
make[1]: *** [_call_image] Error 2
Makefile:192: recipe for target 'image' failed
make: *** [image] Error 2

What configuration step am I missing that will allow the builder to find these packages?