Apex domains cannot have CNAME records.
Question and response
Question
dig grosstable.com. NS
Answer
grosstable.com. 4 NS ns-1420.awsdns-49.org.
grosstable.com. 4 NS ns-1861.awsdns-40.co.uk.
grosstable.com. 4 NS ns-52.awsdns-06.com.
grosstable.com. 4 NS ns-1562.awsdns-03.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0