As some may know, 1.13 will come with a lot of breaking changes. And one of those breaking changes may as well break the entire HeadsPlus plugin, meaning that no heads whatsoever can be spawned in or made, nor can challenges be accessed - effectively making the plugin a shrivelled vegetable.
I have taken some early procautions to avoid these changes from affecting the plugin too much, but this may not be it. The more news I receive, the more I'll make these changes.
P.S: new command soon tm