This tutorial guides you through installing and using Certbot from behind a Cloudflare reverse proxy .

PREREQUISITES

You need a domain

You need to  configure DNS for your domains 

You need  a cloud server

Quick Start

Install Certbot on ubuntu

stop nginx service

generate your certificates

OBTAINING A CERTIFICATE in nginx

Detail steps

Step 1.Configure DNS for your domains 

step 2.stop nginx

step 3.generate your certificates

Certbot （standalone）

sudo certbot certonly

https://www.techaddressed.com/tutorials/certbot-cloudflare-reverse-proxy/