Troubleshooting SSL Certificate installation using Let's Encrypt.

I've attempted to follow the following guide to install SSL certs on my server, however, I'm hitting an error which I'm having trouble isolating the issue.

• https://linode.com/docs/security/ssl/in … tificates/">https://linode.com/docs/security/ssl/install-lets-encrypt-to-create-ssl-certificates/

When Let's Encrypt performs challenges on my domains it fails with the following error: Problem binding to port 80: Could not bind to IPv4 or IPv6.

Searching around, I've found similar issues on other forums but none that resolve my issue.

I'm hoping someone could guide me in a possible direction or help identify possible causes so that I can better debug this issue.