"User denied media access" means that you either blocked access to your mic when you downloaded the PowerCall extension, or you just don't have a mic plugged in and set as the computer's default input/output device.
To rule out not having the mic plugged in, plug in your headset and make sure that it is set as the computer's default input/output, hit "sync microphone" in Kixie PowerCall settings, and make a test call. If it goes through, you're all set.
If you still get user denied media access as an error.... please paste this into your browser: chrome://settings/content#media-stream-mic
Then click manage exceptions and remove the chrome extension item that is blocked from the list of exceptions:
Lastly, make a test call from the dialer and make sure you allow Kixie access to your microphone when prompted, and it should work.