difference between nginx and ddns service

[TheDreadPirate]

A couple things. You need SOMETHING listening on port 80 that will respond to the acme challenge so you can acquire certs. It sounds like you might have that covered.

If have NOT acquired certs already, you will need to comment out all of the letsencrypt lines. Both for the certs and for any SSL/TLS configs, like options-ssl-nginx.conf. Certbot will ADD those lines during the cert request process.