HI.
I know that is not a new problem, but with some other topic can't help me.
Tried to obtain a cerificate with
sudo certbot certonly --standalone
or test
sudo certbot certonly --dry-run
The error is always the same.
The server was stopped (FileMaker on Centos 7)
The ports seem to be free:
s -tlnp | grep -E ":(80|443)"
LISTEN 0 128 [::]:80 [::]:*
LISTEN 0 128 [::]:443 [::]:*
What can I do ?
Welcome to the Let's Encrypt Community 
Standalone spins up its own webserver that tries to listen on port 80. If port 80 is already bound, certbot will fail. Try using --webroot -w /path/to/your/website instead.
Hi.
Thanks, now the certificate is generated and installed (i've used also some tips from the MacOS script installer).
But a new problem, accesing remotely the server seems that the certificate is not valid, accessing local seems it's good.
UPDATE
Now the certificate is valid also remotely, maybe i've just to wait some time. 
Happy it's working!
Usually a stale cache is to blame for not seeing the update.