DNS problem: NXDOMAIN looking up A for domain

Trying add a subdomain in my linode, every time I get this error, how to fix?

[root@li288-249 letsencrypt]# sudo -H ./letsencrypt-auto certonly --standalone -d sub1.mydomain.com.br -d www.sub1.mydomain.com.br
Saving debug log to /var/log/letsencrypt/letsencrypt.log
Plugins selected: Authenticator standalone, Installer None
Obtaining a new certificate
Performing the following challenges:
http-01 challenge for sub1.mydomain.com.br
http-01 challenge for www.sub1.mydomain.com.br
Waiting for verification…
Cleaning up challenges
Failed authorization procedure. www.sub1.mydomain.com.br (http-01): urn:acme:error:dns :: DNS problem: NXDOMAIN looking up A for www.sub1.mydomain.com.br

IMPORTANT NOTES:

• The following errors were reported by the server:

  Domain: www.sub1.mydomain.com.br
  Type: None
  Detail: DNS problem: NXDOMAIN looking up A for
  www.sub1.mydomain.com.br