If you're using the SlingStudio Capture app with a smartphone, and you want to record audio using an external microphone (such as a lavalier or a shotgun mike) you can connect that external microphone directly to the smartphone's audio-in port.
The Capture app should then use the audio from that external microphone. SlingStudio Console treats that external microphone as a part of the combined audio/video source from that smartphone.
If you want to use an external microphone as a separate audio source, you can use the SlingStudio Audio-In port for that purpose. However, you must first connect the external microphone either to an audio mixer, or to a microphone pre-amp, and then connect that to the SlingStudio audio-in port.
Connecting an external microphone directly to the SlingStudio audio-in port does not work.