For anyone else who comes across this thread looking for an answer, the spec for Audio Units plugins (which is what Logic and GarageBand use) does not allow sending MIDI from the plugin into the DAW - this affects any DAW that uses AU plugins (GarageBand, Logic, Reaper, Digital Performer, Ableton Live, Studio One, and others) as the problem is not in the DAW it's in the Audio Units spec. Unfortunately for GarageBand and Logic users, the only plugin format accepted by those programs is AU, but for most other DAWs you can use the VST3 or AAX plugins which do support sending MIDI.

@Rob Helms, in plugin version 3.6.15 we added the function to the AU plugin that when "Send MIDI Data to DAW" is enabled, the plugin sends the MIDI data to the built-in macOS DLSMusicDevice synth. If you don't have any audio out of the BB plugin, then the issue is that most likely the DLSMusicDevice synth is not operating properly, and you should uncheck the "Send MIDI Data to DAW" option in the plugin preferences. Of course, if your plugin is below version 3.6.15 then you should install the latest update from here: https://www.pgmusic.com/support_macintoshupdates.htm

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