Fatal error when using --use-php=system: no alternatives for php-fpm.sock

Debian 10:
[INFO] Settings default system php version.
update-alternatives: error: no alternatives for php-fpm.sock
[ERROR] Exception occured: ISPConfigOSException -> Command update-alternatives --set php-cgi /usr/bin/php-cgi7.3 ; update-alternatives --set php-fpm.sock /run/php/php7.3-fpm.sock failed. (/ispconfig.ai.php:15)

Edited Feb 23, 2021 by Thom

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information