PHP script '/var/www/vhosts/da-manager.com/mod.da-manager.com/plugins/swiftmodders_blesta_theme_installer/swiftmodders_blesta_theme_installer_plugin.php' is protected by SourceGuardian and requires a SourceGuardian loader 'ixed.8.1.lin' to be installed.

1) Download the required loader 'ixed.8.1.lin' from the SourceGuardian site: https://www.sourceguardian.com/loaders/download.php?php_v=8.1.33&php_ts=0&php_is=8&os_s=Linux&os_r=5.15.0-157-generic&os_m=x86_64
2) Install the loader to /opt/plesk/php/8.1/lib/php/modules
3) Edit /var/www/vhosts/system/mod.da-manager.com/etc/php.ini and add 'extension=ixed.8.1.lin' directive