Apex domains cannot have CNAME records.
Question and response
Question
dig sea.tierpoint.com. NS
Answer
sea.tierpoint.com. 2 NS ns1.ral.hostedsolutions.com.
sea.tierpoint.com. 2 NS ns1.bos.hostedsolutions.com.
sea.tierpoint.com. 2 NS ns1.clt.hostedsolutions.com.
sea.tierpoint.com. 2 NS ns1.lit.hostedsolutions.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0