IIS 6: Add a Certificate to a Website
If you have not already done so, add your website certificate by importing it into Windows Server 2003 by read the following post: Windows Server 2003: Import a Certificate into MMC.
To add your certificate
Install Let’s Encrypt on Debian/Ubuntu with Nginx
This post combines several different sources of information on installing Let’s Encrypt on Debian/Ubuntu and configuring SSL on nginx and will show how to install Let’s Encrypt on Ubuntu