When using a headphone jack through my interface (Presonus Audiobox USB 96) I can only hear through my left headphone. I know for a fact it has to do with a miscommunication between my interface and Audacity. My headphones work fine. My inputs and outputs are correct AND I’m recording in mono. Yet every time I playback something I’ve recorded on my microphone (or listen to any audio on any program) it only comes through my left headphone. Ive tried googling so many things and watching videos, and nothing is working. I’m hoping one of you on here can be my savior. 
(or listen to any audio on any program)
That didn’t come out right. If you tell any program, not Audacity, to play sound, it comes out on the left?
This is a Left-Right-Stereo test sound file.
It’s stereo, but play it anyway in Audacity and listen to the headphones. Pay attention to what happens to the Audacity bouncing sound meters.
The main reason for this sound test is the fourth section, but I’m interested in what happens to you in the first three.
Koz