When cloning this repo, please use git clone --recurse-submodules <URI>
.
Without this, the solus secure boot certificate will not be included in the build manifest after a successful build.
If you already have a clone of the systemd repo but have not yet added the git submodule, you can do so with:
git submodule update --init --recursive
This will initialise and fetch an up-to-date version of the submodule into your working copy.