Navigate to Google Search Console and add your domain name;
After additing domain name Google Search Console will provide you with a site ID or verification code;
Copy this code and do not close this tab;
Move back to Site.pro website builder;
Hover over "Settings" menu (at the top of the builder);
Click on "Settings" and switch to "Analytics";
Insert "Google Search Console Verification Code" and click "Apply";
After a few minutes, return to Google Search Console and click "Verify" button.
After adding the code, remember to re-publish your website to activate the verification.