My letsencrypt SSL cert wasn’t renewing. I’d forgotten that I moved my wife’s site to squarespace so that caused the renewal to not find the site on my IP, causing it to fail with something like:

Attempting to renew cert . . .  produced an unexpected error: Failed authorization procedure.

I was using the same cert for multiple sites. Note though, you don’t actually remove the superfluous/relocated sites from the cert and then renew, instead you recreate the cert with just the domains you want. Makes sense.

Anyway, here are some really good instructions and explanation.

And just in case that site isn’t around, basically you’re running:

sudo certbot --cert-name jimwillis.org -d jimwillis.org -d www.jimwillis.org

And then you can run 

sudo certbot certificates

To make sure that the domains were removed from the cert. Handily, it also renews the cert when you run that command.