403 Forbidden caused by AH01630: client denied by server configuration: /data

I am getting this titular error message when following this guide in the Postfix admin section of the tutorial from Apache2's error logs and trying navigate to the website https://mailadmin.example.com/setup.php (also just replaced my website name with example.com) as I'm given a 403 Forbidden.

AH00112: Warning: DocumentRoot [/data/www/mailadmin.example.com/html/public] does not exist
AH00163: Apache/2.4.41 (Ubuntu) OpenSSL/1.1.1f configured -- resuming normal operations
AH01630: client denied by server configuration: /data

Here is my virtual host configuration at sudo nano /etc/apache2/sites-available/mailadmin.example.com-le-ssl.conf :

<IfModule mod_ssl.c>
<VirtualHost *:443>
        ServerName mailadmin.example.com
        ServerAlias mailadmin.example.com
        ServerAdmin [email protected]

        DocumentRoot /data/www/mailadmin.example.com/html/public
        <Directory /data/www/mailadmin.example.com/html/public>
                Options -Indexes +FollowSymLinks
                DirectoryIndex index.php
                AllowOverride All
                Require all granted
        </Directory>

        RewriteEngine on
# Some rewrite rules in this file were disabled on your HTTPS site,
# because they have the potential to create redirection loops.

#       RewriteCond %{SERVER_NAME} =mailadmin.example.com
#       RewriteRule ^ https://%{SERVER_NAME}%{REQUEST_URI} [END,NE,R=permanent]

Include /etc/letsencrypt/options-ssl-apache.conf
SSLCertificateFile /etc/letsencrypt/live/example.com/fullchain.pem
SSLCertificateKeyFile /etc/letsencrypt/live/example.com/privkey.pem
</VirtualHost>
</IfModule>

I'm unaware what this /data means, and I can't find a folder of the sort. I don't see why I'm getting a 403 Forbidden.