Nginx accessing my website with subdomain downloads a file - nginx

Question

While setting up my website using Nginx, and following some instructions from an article, I managed to get the main domain to work. (by typing example.com). My website has also a subdomain (forum.example.com) which instead of launching the forum webpage, it download the main php file instead to which is executed as soon as a request is sent to my server.
This problem also occurs when I type www.forum.example.com but not when I include the https:// prefix for both www.forum.example.com and forum.example.com.
I am not entirely sure why the exampe.com request is working while forum.example.com doesn't. Is there anything I am missing?
I use certbot (let's encrypt) to enable secure connection. Below I am listing the server blocks from the site-enabled directory:
example.com
server {
if ($host = example.com) {
return 301 https://www.example.com$request_uri;
} # managed by Certbot
server_name www.example.com example.com www.forum.example.com forum.example.com;
root /var/www/example/public;
index index.php index.html index.htm;
location / {
try_files $uri $uri/ /index.php?$uri&$args;
}
listen [::]:443 ssl http2 ipv6only=on; # managed by Certbot
listen 443 ssl http2; # managed by Certbot
index index.php index.html index.htm;
location ~ \.php$ {
try_files $uri /index.php?q=$uri&$args =404;
fastcgi_split_path_info ^(.+\.php)(/.+)$;
# NOTE: You should have "cgi.fix_pathinfo = 0;" in php.ini
# With php5-cgi alone:
#fastcgi_pass 127.0.0.1:9000;
# With php5-fpm:
fastcgi_pass unix:/var/run/php/php7.3-fpm.sock;
fastcgi_index index.php;
include fastcgi_params;
fastcgi_param SCRIPT_FILENAME $document_root/$fastcgi_script_name;
}
ssl_certificate /etc/letsencrypt/live/example.com/fullchain.pem; # managed by Certbot
ssl_certificate_key /etc/letsencrypt/live/example.com/privkey.pem; # managed by Certbot
include /etc/letsencrypt/options-ssl-nginx.conf; # managed by Certbot
ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem; # managed by Certbot
}
server {
if ($host = www.example.com) {
return 301 https://www.example.com$request_uri;
} # managed by Certbot
if ($host = example.com) {
return 301 https://www.example.com$request_uri;
} # managed by Certbot
# listen 80 default_server;
server_name localhost;
return 404; # managed by Certbot
}
And the default file:
##
# You should look at the following URL's in order to grasp a solid understanding
# of Nginx configuration files in order to fully unleash the power of Nginx.
# http://wiki.nginx.org/Pitfalls
# http://wiki.nginx.org/QuickStart
# http://wiki.nginx.org/Configuration
#
# Generally, you will want to move this file somewhere, and start with a clean
# file but keep this around for reference. Or just disable in sites-enabled.
#
# Please see /usr/share/doc/nginx-doc/examples/ for more detailed examples.
##
# Default server configuration
#
server {
if ($host = www.example.com) {
return 301 https://$host$request_uri;
} # managed by Certbot
if ($host = example.com) {
return 301 https://$host$request_uri;
} # managed by Certbot
listen 80 default_server;
listen [::]:80 default_server;
# SSL configuration
#
# listen 443 ssl default_server;
# listen [::]:443 ssl default_server;
#
# Note: You should disable gzip for SSL traffic.
# See: https://bugs.debian.org/773332
#
# Read up on ssl_ciphers to ensure a secure configuration.
# See: https://bugs.debian.org/765782
#
# Self signed certs generated by the ssl-cert package
# Don't use them in a production server!
#
# include snippets/snakeoil.conf;
#root /var/www/html;
root /var/www/example/public;
# Add index.php to the list if you are using PHP
index index.php index.html index.htm index.nginx-debian.html;
server_name example.com www.example.com;
location / {
# First attempt to serve request as file, then
# as directory, then fall back to displaying a 404.
try_files $uri $uri/ =404;
# proxy_pass http://localhost:8080;
# proxy_http_version 1.1;
# proxy_set_header Upgrade $http_upgrade;
# proxy_set_header Connection 'upgrade';
# proxy_set_header Host $host;
# proxy_cache_bypass $http_upgrade;
}
# pass the PHP scripts to FastCGI server listening on 127.0.0.1:9000
#
#location ~ \.php$ {
# include snippets/fastcgi-php.conf;
#
# # With php7.0-cgi alone:
# fastcgi_pass 127.0.0.1:9000;
# # With php7.0-fpm:
# fastcgi_pass unix:/run/php/php7.0-fpm.sock;
#}
# deny access to .htaccess files, if Apache's document root
# concurs with nginx's one
#
#location ~ /\.ht {
# deny all;
#}
}
Things I tried include:
changing the order of the server_name values, so by starting with
forum.example.com instead of example.com.
On the first server block, adding an extra if statement in the beginning:
if ($host = forum.example.com) {
return 301 https://forum.example.com$request_uri;
} # managed by Certbot
Another issue I faced was from whichever article I was visiting, they would just tell you to paste the code without really explaining what each method/code block is doing, so I didn't really gain a basic understanding of what is going on. If someone has extra time to explain and help me understand how the requests are being handled and why this error occurs would be much more helpful.
Sidenode: The website is hosted on a VPS server and when I attempt to send a request from the machine I am using right now (example.com) I am seeing the following from Chrome, Firefox and Safari, but when I access example.com from my other devices (iphone, other laptops/computers) I am able to access my website. This assumes all data and cache is cleared from my machine every time I attempt to access my website and from incognito mode.
Please, let me know if more info is needed for me to provide.
Help will be much appreciated!