The harmony playback feature is now available in MuseScore 3 (https://github.com/musescore/MuseScore/pull/5129#issuecomment-601717806) , development of this plugin is thus stopped, thanks for you feedback and positive comments in the past. This plugin for MuseScore 2.0 will expand chords annotations into a few notes in voice 4, directly playable by MuseScore.