Adding an CAA Record
A CAA record lists the certification authorities approved to issue certificats for a domain. Any certification authority that is not listed in a CAA record of a domain, will not be allowed to issue certificates for that domain or any subdomain.
Go to Domains > Details of [example.org] - 🔎 > DNS records,

Administration interface: list of DNS records Choose Add a DNS record,
Fill-in the form.

Administration interface: add an CAA record
Warning
Do not put the root into the Hostname.
For example, by putting www.example.org in this box, you will create a record for www.example.org.example.org.
Three tags are available:
issuewhich allows an authority,issuewildwhich allows an authority for wildcard certificates,iodefwhich gives a URL that certification authorities can contact in case of problems.
Info
Let’s Encrypt certificates are generated for every HTTP address hosted on our servers. They must be authorized.
Some examples
Let’s Encrypt authorization:
» Hostname: [leave blank] » Value: 0 issue "letsencrypt.org" » TTL: 300