Your software
My Mautic version is: 3.0.1
My PHP version is: PHP 7.2.24-0ubuntu0.18.04.6
Server OS: Ubuntu 18.04.4 LTS
Mysql: Ver 14.14 Distrib 5.7.30, for Linux
nginx: nginx/1.14.0 (Ubuntu)
Your problem
My problem is: Seems URL command cannot correctly locate the installer
The command URL changes from domain.com/mautic/ to
domain.com/mautic/index.php/installer with an error 404
These errors are showing in the log: There is no log
Steps I have tried to fix the problem:
1/ i have reviewed other similar error 404 problems and they have not led to solving this particular problem
2/ I assume it is something quite basic in the ngnix config at finding the installer files in the vendor subdir
3/ NOTE: I have a multi-site nginx server with multiple web servers under the main domain.
example: //main domain.com/mautic
//main domain.com/site2
etcâŚ
4/ Suggestion: What may help me (and others with similar configs using nginx) is to post a functional example nginx.conf and perhaps an example site âsites-available/serverâ file so that this step becomes a mute problem for this and future releases.
5/ nginx.conf file: Perhaps someone may be able to point out the errors in my ways 
user www-data;
worker_processes auto;
pid /run/nginx.pid;
include /etc/nginx/modules-enabled/*.conf;
events {
worker_connections 768;
# multi_accept on;
}
http {
##
# Basic Settings
##
sendfile on;
tcp_nopush on;
tcp_nodelay on;
keepalive_timeout 65;
types_hash_max_size 2048;
include /etc/nginx/mime.types;
default_type application/octet-stream;
##
# SSL Settings
##
ssl_protocols TLSv1 TLSv1.1 TLSv1.2; # Dropping SSLv3, ref: POODLE
ssl_prefer_server_ciphers on;
##
# Logging Settings
##
access_log /var/log/nginx/access.log;
error_log /var/log/nginx/error.log;
##
# Virtual Host Configs
##
include /etc/nginx/conf.d/*.conf;
include /etc/nginx/sites-enabled/*;
}
6/ nginx sites-enabled/mautic file
server {
listen 80;
root /var/www/html;
index index.php index.html index.htm index.nginx-debian.html;
server_name mautic;
location = /favicon.ico { log_not_found off; access_log off; }
location = /robots.txt { log_not_found off; access_log off; allow all; }
location ~* .(css|gif|ico|jpeg|jpg|js|png)$ {
expires max;
log_not_found off;
}
location / {
try_files $uri /index.php$is_args$args;
}
location /mautic/ {
try_files $uri $uri/ /mautic/index.php?q=$uri&$args;
}
location ~ \.php$ {
include snippets/fastcgi-php.conf;
fastcgi_pass unix:/var/run/php/php7.2-fpm.sock;
fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
include fastcgi_params;
fastcgi_split_path_info ^(.+.php)(/.+)$;
}
}
Many Thanks for any input and suggestions on thisâŚ
Rgs