When debug mode is enabled (Downloads > Settings > Misc > General), specific information will be logged to a custom log file on your site. Developers can make use of this to help troubleshoot issues and results at specific points in their code.
edd_debug_log( $message = '', $force = false );
$message: This must be a string, and it’s exactly what will show in the log file.
$force: Use the function with this parameter set to
trueto force your message to be added to the log file, even if debug mode is not enabled. Use this only for critical messages and warnings.