As you can see, at the bottom of the signup page, it is loading the security question (ReCAPTCHA). But the error message is telling you that Moodle can’t communicate with the ReCAPTCHA server. Have you got the curl extension installed and enabled in php? Have you registered your domain with Google ReCAPTCHA?
See
- https://docs.moodle.org/36/en/admin/environment/php_extension/curl
- https://docs.moodle.org/36/en/Managing_authentication#ReCAPTCHA
See
- https://docs.moodle.org/36/en/admin/environment/php_extension/curl
- https://docs.moodle.org/36/en/Managing_authentication#ReCAPTCHA
ps. This forum is for the Feedback activity in Moodle. You'll maybe get a better response in the General Help forum.