Apex domains cannot have CNAME records.
Question and response
Question
dig managedservice.io. NS
Answer
managedservice.io. 5 NS service.g1-dns.com.
managedservice.io. 5 NS service.g1-dns.one.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0