Apex domains cannot have CNAME records.
Question and response
Question
dig wpci-hosting.de. NS
Answer
wpci-hosting.de. 4 NS ns2.wpci-hosting.de.
wpci-hosting.de. 4 NS ns3.wpci-hosting.de.
wpci-hosting.de. 4 NS ns1.wpci-hosting.de.
Authority
The response has no authority records.
Additional
ns1.wpci-hosting.de. 4 A 109.237.142.8
ns2.wpci-hosting.de. 4 A 148.251.254.105
ns3.wpci-hosting.de. 4 A 109.237.143.8
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0