Is there a snipped for Roundcube available? This one at https://www.howtoforge.com/using-roundcube-webmail-with-ispconfig-3-on-debian-wheezy-nginx ends with an 500 error
The snippet should work when you adjust the path to the php-fpm socket: fastcgi_pass unix:/var/run/php5-fpm.sock; to match the new path for php 7on Ubuntu 16.04.
I already did change it to: fastcgi_pass unix:/var/run/php/php7.0-fpm.sock But still had the 500 error