Thank you for using Bitnami. As the guide says, it assumes that you have already registered a domain name and set a DNS record pointing that domain name to the public IP address of your WordPress server, is that correct? Are you using your own domain when generating the certificate?
Apart from that, could you please share the output of the following command?
sudo ls -la /opt/bitnami/apps/wordpress/letsencrypt/live/account/
Regarding this information, could you please let us know the version of WordPress and WP encrypt plugin that you're using?