Hi,
The error message indicates that the key you've configured in the settings of the plugin is incorrect. So I would recommend verifying it in your ReCaptcha account and use the correct type of key (v2) linked to the correct URL of the website when configuring the plugin :
stackoverflow.com/questions/53108522/goo...ner-invalid-key-type
Also, with the advances in AI in the past few years, ReCaptcha and other captcha solutions are less and less useful to prevent spam.
I would recommend switching to OSpam-a-not:
extensions.joomla.org/extension/ospam-a-not/
It is easier for the user as they don't have to do anything, and spam bots have a harder time circumventing it due to the way it works.