Problem getting sound through headphones running 2.2.2 on macOS High Sierra

I have just moved over to a new MacBook Pro with High Sierra (10.13.6). I tried playing back an Audacity project on Audacity Version 2.2.2 with headphones plugged in. I took my headphones off while the sound was playing, and realized the sound was coming out of the built-in speakers (on the MacBook Pro). In fact, I don't think it was even coming out of the headphones. It just seemed like it at first. 

I checked that the headphones were completely plugged in to the headphone port (they were). 

I checked in System Preferences > Sound, and it showed that the headphones were plugged in, and selected. 

I went back to Audacity and checked the Playback Device setting, and it said MacBook Pro Speakers, and did not have an option for headphones. I went to Audacity > Preferences, and selected Devices. 

Under Interface it says: Host is Core Audio (no other option) using PortAudio V19.5.0-devel, revision unknown. 

Under Playback it says: Device: MacBook Pro Speakers (no other option). 

I'm wondering how I can add headphones to the playback device list so that sound only comes out the headphones when I have them plugged in. 

I migrated all my apps. from an older Mac, running El Capitan (10.11), running this same version of Audacity (2.2.2), and had no problem with this. I thought maybe the migration hadn't gone well for Audacity, so I uninstalled it, and tried reinstalling. I still have the same problem. 

Thanks for any suggestions. 

---Mark 
[email protected]

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