WARNING - Let's Encrypt SSL Cert for: domain.tld could not be issued

Hi,
I've just upgraded ISPCONFIG3.0 to 3.1 (with the ispconfig_update.sh script) to use the new "let's encrypt" automated feature.
I tried with an existing website the feature, but when I checked "Let's Encrypt SSL" checkbox (checking this box automatically check the "SSL" box) and save, nothing happens. When I select again the website, the checkboxes are again unchecked.
Turning on the debug ispconfig log, I found this:
"WARNING - Let's Encrypt SSL Cert for: domain.tld could not be issued."
I've read the manual but I didn't find a clue to solve this. I'm using debian Wheezy.
Can I have some help?
Regards,

 

No, I thought that the updater did this.
Ok, I'll install it
Thank you

 

Step 11: https://www.howtoforge.com/tutorial...4-jessie-apache-bind-dovecot-ispconfig-3-1/2/