Apex domains cannot have CNAME records.
Question and response
Question
dig grassregistries.com. NS
Answer
grassregistries.com. 4 NS ns3.blacknight.com.
grassregistries.com. 4 NS ns1.blacknight.com.
grassregistries.com. 4 NS ns2.blacknight.com.
grassregistries.com. 4 NS ns4.blacknight.com.
Authority
The response has no authority records.
Additional
ns1.blacknight.com. 4 A 78.153.212.176
ns2.blacknight.com. 4 A 81.17.254.6
ns3.blacknight.com. 4 A 185.28.194.194
ns4.blacknight.com. 4 A 185.38.108.108
ns2.blacknight.com. 4 AAAA 2a01:a8:dc3:3313:0:0:0:aaaa
ns3.blacknight.com. 4 AAAA 2a00:fea0:dead:0:0:0:0:beef
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0