Struggling to use Key Detect with Spotify

[greenmoss]

I've just purchased Key Detect to find the keys of songs from my Spotify playlist. I know it should be easy and intuitive, but I can't see how it works. Where are the instructions? I'm using it to pair my guitar music with appropriate songs from Spotify. Any assistance would be very welcome.

[discopex]

It uses the phone microphone to listen to a music source (which cannot be the very same phone). If it doesn't recognize the music there must be something wrong with the audio input setting in the phone.