I managed to resolve this problem by setting up my ssl certificate manually with nginx and letsencrypt-auto (GitHub - certbot/certbot: Certbot is EFF's tool to obtain certs from Let's Encrypt and (optionally) auto-enable HTTPS on your server. It can also act as a client for any other CA that uses the ACME protocol.)
The command I used after cloning letsencrypt repo in /opt/:
/opt/letsencrypt$ ./letsencrypt-auto certonly -a manual --rsa-key-size 4096 --email youremail@here.com -d yourdomainhere.com -d www.yourdomainhere.com
I did this while running in terminal with GNU screen so I could manually create the files required by certbot.
Also I had a properly configured nginx, with listen 443 ssl; in the config file.
By the way, I want to thank everyone that answered this post.
See ya! 