Apex domains cannot have CNAME records.
Question and response
Question
dig mkt31.net. NS
Answer
mkt31.net. 5 NS ns-1614.awsdns-09.co.uk.
mkt31.net. 5 NS ns-635.awsdns-15.net.
mkt31.net. 5 NS ns-237.awsdns-29.com.
mkt31.net. 5 NS ns-1297.awsdns-34.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0