Update 2.9.69 solved the issue. Thanks!
Hi, I created a new thread in https://www.wpdownloadmanager.com/support/topic/using-captcha-returns-undefined-message/
Thanks.
Same issue here, “Undefined” message is shown after clicking on captcha checkbox. Downloading works if captcha is disabled. Using WP Download Manager 2.9.68 and WordPress 4.9.4.