As I suspected, the problem was a combination of problems in my generated json file (empty targets) and problems with the plugin.
After some joint work with Kingsley Hendrickse (the author of the plugin), a new version of the plugin was released (0.0.20), which fixed all these problems!
The plugin page is here.
I want to publicly thank Kingsley for his help and support!
I hope somone finds this post useful.