Hello MarcosOkay,
If you get the error message of "Failed to start audio capture", please refer to the following solution.
https://www.bandicam.com/faqs/failed-to ... o-capture/
If it does not seem to work, please attach screenshots of the Bandicam Recording settings window and Windows Sound settings window.
Also, please let us know your recording target and how to recreate your issue.
Thank you.