You cannot use the built-in mic on the smartphone or tablet that is used for streaming. Please use the mic on the GO:PODCAST unit or on the iPhone/iPad used as a satellite camera for audio input.
Alternatively, you can add audio files (background music, sound effects, etc.) from your smartphone to use as materials when streaming to the GO:PODCAST app. For details on importing files, please refer to "Adding still images, videos, and audio to a scene" in the GO:PODCAST app Owner's Manual.