If you're using RECAP S2 and your voice is not being recorded while the other voice is, that typically means that the recording device is not providing the "biasing voltage" to RECAP. To fix that, you need to ensure that your recording device is setup to operate with an external stereo microphone.

If you have a computer, this article may help: http://www.recapmycalls.com/recap-support/adjust-microphone-volume/

If you're using a digital voice recorder, check the user's manual and look for the "external stereo microphone" configuration.

Additional tips

- A good way to make test calls is using Skype's free "Sound Test Service"  link. That is done via the Skype app. It places a free call to Skype, and ask you to record a message, which is then played back to you. 

- Analyze the captured recording in a tool like Audacity. Note amplitude of the problematic channel. You may find the issue is not with the bias voltage, but maybe with a poor performance of the microphone in your headset.