Okay, so it seems you are both running non-standard configurations. Both times, your web server user is lacking group membership in the group pihole.
Not sure which user your web servers are running as (typical for lighttpd is www-data). Try to find out which is the correct web server user and add it to group pihole. Thereafter, restart your web server and try again. If this is not sufficient to communicate the new group membership (it should be), you might have to restart your system.