Go to URL https://www.google.com/u/3/recaptcha/admin/create
Login to Client gmail account
And add a new site and enter the domain name.

Pick reCAPTCHA v2 as this is the one compatible with Gravity forms.
Here I prefer to use the Invisible Recpatcha as it’s a cleaner one and doesn’t clutter the page so I check this one.

Once you submit the above values you will be given two keys: Site Key and Secret key, copy and paste them into Gravity forms as below.

In the WP admin go to Gravity forms and then Settings where you will find a Recaptcha section.
Paste the two site keys obtained above and select Invisible next to it and then click Save.

Save the Keys to Keypass when completed.