Apex domains cannot have CNAME records.
Question and response
Question
dig caribbeanembeddedlabs.com. NS
Answer
caribbeanembeddedlabs.com. 5 NS ns1025.ui-dns.de.
caribbeanembeddedlabs.com. 5 NS ns1045.ui-dns.biz.
caribbeanembeddedlabs.com. 5 NS ns1030.ui-dns.com.
caribbeanembeddedlabs.com. 5 NS ns1098.ui-dns.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0