Hi Matthews
That means Captcha is not setup properly on your site. Could you please follow the instruction at
documentation.joomdonation.com/2-events-...116-use-captcha.html
to setup Captcha (the instruction was written for a different extension but it works the same )
If you still could not get it setup properly, please submit a support ticket sending us super admin account of your site so that we can setup it for you
Regards,
Tuan