Recaptcha

Hi, I'm trying to install a recaptcha plugin (Fast Secure Recaptcha) on my site but for some reason the recaptcha window doesn't show up which makes it impossible to write a comment without getting an error. I've entered the secret key and site key. I've added this <script src='https://www.google.com/recaptcha/api.js'></script> to the </head> tag. And added <div class="g-recaptcha" data-sitekey="6Lf89gkUAAAAAGU-HjFPP3QHItw5KCFyaxa9WcKj"></div> to the comment form. I don't know what's missing. Is the theme compatible with recaptcha? All the best Casper