Apache2: Forbidden You don't have permission to access /dir/ on this server

Let's make the vhost clear:

<VirtualHost *:80>
    ServerAdmin webmaster@localhost

    DocumentRoot /var/www
    <Directory />
        Options FollowSymLinks
        AllowOverride None
    </Directory>
    <Directory /var/www/>
        Options Indexes FollowSymLinks MultiViews
        AllowOverride None
        Order allow,deny
        allow from all
    </Directory>

    ScriptAlias /cgi-bin/ /usr/lib/cgi-bin/
    <Directory "/usr/lib/cgi-bin">
        AllowOverride None
        Options +ExecCGI -MultiViews +SymLinksIfOwnerMatch
        Order allow,deny
        Allow from all
    </Directory>

    ErrorLog ${APACHE_LOG_DIR}/error.log

    # Possible values include: debug, info, notice, warn, error, crit,
    # alert, emerg.
    LogLevel warn

    CustomLog ${APACHE_LOG_DIR}/access.log combined
</VirtualHost>

Then make sure you set the right permission like this:

sudo adduser <username> www-data
sudo chown -R www-data:www-data /var/www
sudo chmod -R g+rw /var/www

This works for me, very well:

<Directory "/var/www">
    AllowOverride None
    Require all granted
</Directory>

Checkout this tutorial: https://www.tecmint.com/forbidden-you-dont-have-permission-to-access-on-this-server-error/