Apex domains cannot have CNAME records.
Question and response
Question
dig previewmymobile.com. NS
Answer
previewmymobile.com. 5 NS ns-1345.awsdns-40.org.
previewmymobile.com. 5 NS ns-913.awsdns-50.net.
previewmymobile.com. 5 NS ns-31.awsdns-03.com.
previewmymobile.com. 5 NS ns-1702.awsdns-20.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0