Adding Lets Encrypt for Multiple Domain on same server Ubuntu 18.0 in case

That requires a skill set to modify a file that has all the information related to modification

Most Probably under normal cases resides below

/etc/apache2/sites-available/000-default-le-ssl.conf

The SSL needs to be renewed like below ( requires certbot to be installed )

sudo certbot --apache -d gatoon.org -d www.gatoon.org 

The entire virtual hosts file looks like

<VirtualHost *:443>
        ServerAdmin webmaster@localhost
        DocumentRoot /var/www/html

        ErrorLog ${APACHE_LOG_DIR}/error.log
        CustomLog ${APACHE_LOG_DIR}/access.log combined

ServerName gatoon.com
Include /etc/letsencrypt/options-ssl-apache.conf
ServerAlias www.gatoon.com
SSLCertificateFile /etc/letsencrypt/live/gatoon.com/fullchain.pem
SSLCertificateKeyFile /etc/letsencrypt/live/gatoon.com/privkey.pem
</VirtualHost>

<VirtualHost *:443>
        ServerAdmin webmaster@localhost
        DocumentRoot /var/www/html

        ErrorLog ${APACHE_LOG_DIR}/error.log
        CustomLog ${APACHE_LOG_DIR}/access.log combined

ServerName gatoon.net
Include /etc/letsencrypt/options-ssl-apache.conf
ServerAlias www.gatoon.net
SSLCertificateFile /etc/letsencrypt/live/gatoon.net/fullchain.pem
SSLCertificateKeyFile /etc/letsencrypt/live/gatoon.net/privkey.pem
</VirtualHost>

<VirtualHost *:443>
        ServerAdmin webmaster@localhost
        DocumentRoot /var/www/html

        ErrorLog ${APACHE_LOG_DIR}/error.log
        CustomLog ${APACHE_LOG_DIR}/access.log combined

ServerName gatoon.org
Include /etc/letsencrypt/options-ssl-apache.conf
ServerAlias www.gatoon.org
SSLCertificateFile /etc/letsencrypt/live/gatoon.org/fullchain.pem
SSLCertificateKeyFile /etc/letsencrypt/live/gatoon.org/privkey.pem
</VirtualHost>