To generate a Site Key and a Secret Key, please follow the steps:
To check how the reCaptcha works, please, follow the steps:
1. Open the page where reCapthca should be; 2. Open browser console (Shift+Ctrl+I); 3. Open Console settings:
4. Uncheck 'Select Automatically' and choose any kind of browser or device; 5. Fill in and submit the form.
However, Google uses its own criteria to define whether a real man or a spam-bot is trying to send you a message. One of this criteria is the user agent. ReCapthca shows the verification pictures only if it suspects a bot.
This error message is related to the default Magento or third-party captcha. When you use a custom theme, it hides "I'm not a robot" checkbox and it's not available for submitting. Therefore, ''Incorrect CAPTCHA'' message is displayed.
The solution is pretty easy: just disable the default Magento or third-party captcha. The ''Incorrect CAPTCHA'' message should be gone. If it still appears, please do not hesitate to create a support ticket.
Having submitted the form and when the badge of Google Invisible reCaptcha appears, one may not be redirected to the successful page as there is a possibility of a third-party CAPTCHA working on the same page.