"Enable captcha" option in configuration

I am confused about what the option "Enable captcha" is actually doing.  tooltip for Enable captcha option  I found that when this is enabled, and I have ALSO enabled the use of CAPTCHA - Invisible reCAPTCHA on the site (Global Config) with Joomla 5.1 AND I have enabled the "CAPTCHA - Invisible reCAPTCHA" plugin registrations FAIL with the message "Invalid verification code entered" for SOME credit cards ALL of the time, for some credit cards when more than one registrant is being registered for the event and never for some credit cards.

I DISABLED the Events Booking CAPTCHA and we didn't see that error message anymore. However, I don't know DISABLING CAPTCHA means that there is NO CAPTCHA protection from bots, or only that the global CAPTCHA is used rather than an Event Booking specific CAPTCHA or something else that I haven't thought of. The tooltip is not saying anything meaningful. My first guess based upon that tooltip was that enabling CAPTCHA in the EB configuration would simply display the recapture badge    .
Indeed, disabling the captcha within Event Booking DOES disable the display of the captcha - recaptcha badge - but it is not clear whether the form is then completely unprotected from bots or if there is still protection from the System configuration of Invisible Capture.

The message in English - "Invalid verification code entered" is somewhat vague and misleading. Most visitors think that the 'verification code' refers to the credit card's CVV number while it actually means that the CAPTCHA has failed to determine that the visitor is human.

Clarification of what happens when "Enable captcha" is set to YES or NO would be very helpful. 
Changing the description in the tooltip associated with "Enable captcha" would be very helpful.
Changing the message displayed so it indicates that the CAPTCHA failed to determine that the visitor is human (if that actually is what it is supposed mean) would be very helpful.

I haven't yet had a chance to examine this issue with Joom Donation, however, I have seen the same message "Invalid verification code entered" when testing with one credit card and not with a different credit card. I suspect that the same special CAPTCHA as Event Booking and that it is not working very well for either EB or Joom Donation.