Apex domains cannot have CNAME records.
Question and response
Question
dig o4s-hosting.nl. NS
Answer
o4s-hosting.nl. 5 NS nsauth3.truezuid.nl.
o4s-hosting.nl. 5 NS ns0.o4s.nl.
o4s-hosting.nl. 5 NS nsauth2.truezuid.nl.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0