It produced this output:
nginx: [emerg] BIO_new_file("/etc/letsencrypt/live/prueba.com/fullchain.pem") failed (SSL: error:02001002:system library:fopen:No such file or directory:fopen(’/etc/letsencrypt/live/pruebahost.com/fullchain.pem’,‘r’) error:2006D080:BIO routines:BIO_new_file:no such file)
nginx: configuration file /etc/nginx/nginx.conf test failed
My web server is (include version): A virtual Machine
The operating system my web server runs on is (include version): ubuntu 16.04
My hosting provider, if applicable, is: It is a local host, I’m trying to set up a web server with Nginx, php, mysql and wordpress on a Virtual Machine
I can login to a root shell on my machine (yes or no, or I don’t know): Yes
I’m using a control panel to manage my site (no, or provide the name and version of the control panel):
The version of my client is (e.g. output of certbot --version or certbot-auto --version if you’re using Certbot): certbot 0.23.0
Is the problem that pruebahost.com is not really your domain, but a domain that you were using as a test?
If you don't have your own domain name, you should look for a tutorial about creating a self-signed certificate rather than requesting a certificate from Let's Encrypt, since Let's Encrypt issues only publicly-trusted certificates (and must confirm that the recipient of the certificate controls the domains listed in the certificate).