The reason why you're getting that error is because xBilling back end still calls zPanel instead of Sentora sometimes, so you need to find the file you're getting the issue on, and hard code from zPanel to Sentora.
nano or vi this file: /etc/sentora/panel/modules/xbilling/code/controller.ext.php
change this line : static $module_db = 'zpanel_xbilling'; to static $module_db = 'sentora_xbilling';
change $server_app = 'zpanel'; to $server_app = 'sentora';
Bam! Blank page problem fixed. This also fixes your not being able to download the config file/save changes/etc
nano or vi this file: /etc/sentora/panel/modules/xbilling/code/controller.ext.php
change this line : static $module_db = 'zpanel_xbilling'; to static $module_db = 'sentora_xbilling';
change $server_app = 'zpanel'; to $server_app = 'sentora';
Bam! Blank page problem fixed. This also fixes your not being able to download the config file/save changes/etc
Development:
Sentora WHMCS Addon - Started
Sentora ClamAV Virus Scanner Plugin - Not Started
Sentora WHMCS Addon - Started
Sentora ClamAV Virus Scanner Plugin - Not Started