google-robot-captcha

I tried to implement a WebsiteMemberManagement signup page employing the code provided some time ago in Dave's 

sample-user-signup-form-with-google-robot-captcha.php code.

The Captcha checkbox from Google draws on the page, but has the error:

ERROR for site owner: Invalid key type

I have new v3 keys and had understood that this code worked with v3. Am I mistaken about this?

Feedback from anyone else who has used this is appreciated.