Export to mono .mp3

I need to export to a mono file .mp3 file (128 kbps). But only the “joint stereo” and “stereo” options are available. What should I do?

Stereo/Joint Stereo are ignored if the track is already mono and not panned to left or right. A single channel file will be exported.

In the next 2.1.3 version of Audacity when released there will be a “Force export to mono” checkbox for when you have a stereo track, but a mono file will still be exported from a mono track even if that checkbox is not enabled.