Apex domains cannot have CNAME records.
Question and response
Question
dig openprovider.nl. NS
Answer
openprovider.nl. 4 NS ns-eu-west-2.openprovider.eu.
openprovider.nl. 4 NS ns-eu-central-1.openprovider.eu.
openprovider.nl. 4 NS ns-eu-west-1.openprovider.eu.
Authority
The response has no authority records.
Additional
ns-eu-west-1.openprovider.eu. 4 A 52.19.66.106
ns-eu-west-2.openprovider.eu. 4 A 52.56.180.255
ns-eu-central-1.openprovider.eu. 4 A 18.194.228.62
ns-eu-west-1.openprovider.eu. 4 AAAA 2a05:d018:61d:bd00:c886:556d:56a4:db8b
ns-eu-west-2.openprovider.eu. 4 AAAA 2a05:d01c:433:e000:9d6a:209f:a4ad:3c7
ns-eu-central-1.openprovider.eu. 4 AAAA 2a05:d014:f80:6e00:b20f:a574:7f25:31ad
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0