How to configure Captcha API Settings?
Step 1 First, you need to have an API key, for this, go to https://www.google.com/recaptcha/admin. To gain access to this page, you’ll need to be logged into a Google account. You’ll be asked to register your website, so give it a suitable name, then list domains (for example tutsplus.com) where this particular reCAPTCHA will be used. Subdomains (such as webdesign.tutsplus.com and code.tutsplus.com) are automatically taken into account.
Step 2 Once done, you’ll be given a site key and its partner secret key:
Copy and paste both site key and secret key by logging-in to your site under wp-admin /WP DB/ settings / api settings /reCaptcha and you are done with configurations.