Enabling Let's Encrypt

Hi

I am trying to enable LetsEncrypt on a already running ISPConfig 3.1.2
I have added the needed packages (from a jessy backport repo):

dpkg --list | grep -i -E 'certbot|lets'
ii certbot 0.10.2-1~bpo8+1 all automatically configure HTTPS using Let's Encrypt
ii letsencrypt 0.10.2-1~bpo8+1 all transitional dummy package
ii python-certbot 0.10.2-1~bpo8+1 all main library for certbot​

and tried to reconfgiure ISPConfig with: php -q update.php
But still there is no Let's Encrypt tab in site settings (only the regular SSL one). Any suggestions what else to check would be welcomed.