To set up Captcha verification go to the Widget tab > Edit widget.
​
In the Calls tab click on the Captcha verification:
​

​

Now you can create the captcha keys, here.

Use the label that will make it easy for you to identify the site in the future:
​

Go to the reCAPTCHA type and choose Challenge (v2) and "I'm not a robot" Checkbox:
​

Add the domain where you want to apply Captcha verification:
​

Submit and copy both keys and pas them in the CallPage panel:
​

​
​

And the last step is to Save changes.
​

​