Hello,
Please refer to the following FAQ, first.
https://www.bandicam.com/faqs/how_to_re ... icrophone/
Please also refer to the "A comparison between the registered and the unregistered version" section on the linked page.
https://www.bandicam.com/downloads/
If you still have the same issue, please attach screenshots of the Bandicam Recording settings window and Windows Sound settings window.
Please create a new account if you have an additional inquiry since you cannot use the account any more.
Thank you.