a1.billingbooth.com has no CNAME records.
Question and response
Question
dig a1.billingbooth.com. NS
Answer
The response has no answer records.
Authority
billingbooth.com. 444 SOA ivy.ns.cloudflare.com. dns.cloudflare.com. 2397142555 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0