# /usr/sbin/lighttpd -tt -f /etc/lighttpd/lighttpd.conf
2021-12-06 15:14:18: plugin.c.195) dlopen() failed for: /usr/lib/lighttpd/mod_openssl.so /usr/lib/lighttpd/mod_openssl.so: cannot open shared object file: No such file or directory
2021-12-06 15:14:18: server.c.1238) loading plugins finally failed
It looks like the openssl module for lighttpd is missing.
Edit: upon searching I found this solution that works for me:
# apt install lighttpd-mod-openssl
https://dietpi.com/forum/t/enabling-ssl-for-internal-network/5861/9
Now I get a 400 Bad Request response when going to the /admin webpage in a browser. I’ll poke around the settings more.