Apex domains cannot have CNAME records.
Question and response
Question
dig thryvinc-ns.com. NS
Answer
thryvinc-ns.com. 5 NS ns1.thryvinc-ns.com.
thryvinc-ns.com. 5 NS ns3.thryvinc-ns.com.
thryvinc-ns.com. 5 NS ns2.thryvinc-ns.com.
Authority
The response has no authority records.
Additional
ns1.thryvinc-ns.com. 5 A 198.41.222.155
ns2.thryvinc-ns.com. 5 A 162.159.10.178
ns3.thryvinc-ns.com. 5 A 162.159.11.220
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0