ReCaptcha from Comment Spam Pack asking for API key

After I installed the comment spam pack and activated the ReCAPTCHA plugin, I get a message below the comment form saying this:

To use reCAPTCHA you must get an API key from

I get to the site, create an API key, but I can't find where to input that key into any configuration pages for this plugin. Where is it or what am I doing wrong?