• need Certbot to use Let's Encrypt to get a SSL certificate
• sudo vim /etc/apt/sources.list

  # Add this on the bottom of the file
  deb http://deb.debian.org/debian stretch-backports main contrib non-free
  deb-src http://deb.debian.org/debian stretch-backports main contrib non-free

• sudo apt update
• sudo apt install python-certbot-nginx -t stretch-backports
• certificate is active only for 90 days, auto renewall enable sudo certbot renew --dry-run

Resources:

➡️https://www.digitalocean.com/community/tutorials/how-to-secure-nginx-with-let-s-encrypt-on-debian-9