Is Lets-Box successfully linked to your Box account? If this isn’t the case read the installation instructions how to reauthorize Lets-Box.
When the plugin is successfully authorized, you are not able to see your files in the File Browser or on the Folder tab in the Shortcode Builder, the plugin is probably encounter difficulties to obtain the File List. There can be multiple reasons for this.
To identify what is going on, please first make sure that you are running the latest version of the plugin. Perhaps the issue is caused by a bug in the plugin which is already solved!
If the problem persists after updating the plugin, please enable the WP_DEBUG setting in the wp-config.php file of your WordPress installation. If the error messages of WP_DEBUG don't help you to solve the problem, or if you don't see any error messages at all, feel free to submit a support ticket and attach the debug.log file (If larger than 1MB, please use wetransfer.com)! We do our best to help you as quickly as possible!