Apex domains cannot have CNAME records.
Question and response
Question
dig cm.puzzel.com. NS
Answer
cm.puzzel.com. 5 NS ns-853.awsdns-42.net.
cm.puzzel.com. 5 NS ns-1150.awsdns-15.org.
cm.puzzel.com. 5 NS ns-1845.awsdns-38.co.uk.
cm.puzzel.com. 5 NS ns-395.awsdns-49.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0