ERROR for site owner: Invalid key type error on the contact page.
Verify that the keys are correct here - https://www.google.com/recaptcha/admin#list. If keys are correct, but the problem still remains, try to generate new keys and enter them on the plugin settings page.
After this try to follow the next instructions in order to test reCaptcha's keys:
1. Go to reCaptcha Settings page;
2. Click "Test reCaptcha";
3. Test your reCaptcha;
4. Then сlick "Test Verification";
Also, it's necessary to check reCAPTCHA version because if you switched between Version 2 and Version 3, you should regenerate new keys.