Theme plugin: How to integrate logos

I am currently struggling with them plugin (modeled after the cern theme plugins):

    + indico_mlz_themes

in the theme scss I try to use (with different variants for the prefix:
include header-logo('mlz_lecture:logo.png', 15px 45px, 200px);

While the generated html is mostly correct, the image is never found. The only way that seems to work is
using a hardcoded path and putting the logo into /static/custom manually.

Where am I doing the wrong thing?

since you are most likely on 2.1 (2.2/master is not production ready, at least when using room booking!), you need to base your plugin on the code we have in the 2.0-maintenance branch of the plugin repo (2.0 plugins are for indico 2.1)

Thanks, that was it.