Apex domains cannot have CNAME records.
Question and response
Question
dig pool.ictprovider.nl. NS
Answer
pool.ictprovider.nl. 5 NS dns3.sollie.nl.
pool.ictprovider.nl. 5 NS dns2.sollie.nl.
pool.ictprovider.nl. 5 NS dns1.sollie.nl.
Authority
The response has no authority records.
Additional
dns1.sollie.nl. 4 A 185.102.44.18
dns2.sollie.nl. 4 A 185.102.45.18
dns3.sollie.nl. 4 A 77.222.78.93
dns1.sollie.nl. 4 AAAA 2a0b:7e40:0:120:440d:ed7c:cc47:4e91
dns2.sollie.nl. 4 AAAA 2a0b:7e40:0:121:fc94:b984:9dbb:4798
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0