Fresh install, FastCGI sent in stderr: "Primary script unknown" errors

I am doing a fresh install using https://docs.librenms.org/Installation/Installation-Ubuntu-1804-Nginx/ and am getting this error:

2020/08/21 13:14:49 [error] 846#846: *14 FastCGI sent in stderr: "Primary script unknown" while reading response header from upstream, client: 192.168.2.22, server: librenms.beachops.io, request: "GET /install.php HTTP/1.1", upstream: "fastcgi://unix:/var/run/php/php7.2-fpm.sock:", host: "librenms.beachops.io"

I’ve spent about an hour trying to debug this and must be missing something. Any pointers?