Are you trying to listen to the audio on the goggles during playback, or from an external device? If you’re listening for the audio while watching back a recording in the playback mode of the device, the Spy Net goggles unfortunately do not have that capability. You are able to watch back the video, but the speaker on the device is not capable of playing back the audio. Be assured, however, that the audio is being recorded. In order to hear the audio from the device, you must play back the video on a computer.
If you are viewing the recordings on a computer and the audio is still not playing back, then the problem is more than likely due to a faulty microphone. Follow along with this guide for information on how to replace the microphone.