Failed authorization procedure _ Please help

[shishirms]

Please fill out the fields below so we can help you better.

My domain is: my.example.com

I ran this command: ./letsencrypt-auto --apache -d my.example.com

It produced this output:
root@VM-MEngine:/opt/letsencrypt# ./letsencrypt-auto --apache -d my.example.com
Saving debug log to /var/log/letsencrypt/letsencrypt.log
Obtaining a new certificate
Performing the following challenges:
tls-sni-01 challenge for my.example.com
Enabled Apache socache_shmcb module
Enabled Apache ssl module
Waiting for verification…
Cleaning up challenges
Failed authorization procedure. my.example.com (tls-sni-01): urn:acme:error:connection :: The server could not connect to the client to verify the domain :: Timeout

IMPORTANT NOTES:

• The following errors were reported by the server:

  Domain: my.example.com
  Type: connection
  Detail: Timeout

  To fix these errors, please make sure that your domain name was
  entered correctly and the DNS A/AAAA record(s) for that domain
  contain(s) the right IP address. Additionally, please check that
  your computer has a publicly routable IP address and that no
  firewalls are preventing the server from communicating with the
  client. If you’re using the webroot plugin, you should also verify
  that you are serving files from the webroot path you provided.

My web server is (include version): apache2

The operating system my web server runs on is (include version): Ubuntu 14.04.5

My hosting provider, if applicable, is:

I can login to a root shell on my machine (yes or no, or I don’t know): yes

I’m using a control panel to manage my site (no, or provide the name and version of the control panel): no

[Osiris]

Do you have port 443 open in your firewall or properly opened/port mapped in case of a NAT router?

[shishirms]

443 port was not open. After opening the port, issue got resolved.

Thanks a lot for your help Osiris.