Let's Encrypt error

I am trying to run let’s encrypt to generate my certificates. I am trying to run MATRIX Synapse.
I have local install

My domain is local.net
My Machine name: freedombox.local.net

Steps to Reproduce
System> Let’s encrypt> obtain

Expected Results
I expected to see a message confirming certificates were generated

Actual results

When I am trying to obtain new certificates, freedombox show me next error

I checked /var/log/letsencrypt/letsencrypt.log and show next:


Sorry, but the forum don’t let me show two pics at same message

Hi! Your domain has to be publicly visible from the Internet to have a LE certificate.