Apex domains cannot have CNAME records.
Question and response
Question
dig api.oxxa.com. NS
Answer
api.oxxa.com. 5 NS ns3.satserver.nl.
api.oxxa.com. 5 NS ns1.satserver.nl.
api.oxxa.com. 5 NS ns2.satserver.nl.
Authority
The response has no authority records.
Additional
ns1.satserver.nl. 5 A 87.236.96.11
ns2.satserver.nl. 5 A 87.236.99.22
ns2.satserver.nl. 5 A 185.145.63.232
ns3.satserver.nl. 5 A 87.236.98.33
ns3.satserver.nl. 5 A 185.10.51.44
ns1.satserver.nl. 5 AAAA 2a02:cc8:11:0:0:0:0:11
ns2.satserver.nl. 5 AAAA 2a02:cc8:22:0:0:0:0:22
ns2.satserver.nl. 5 AAAA 2a02:cc9:0:63:0:0:0:232
ns3.satserver.nl. 5 AAAA 2001:470:1f15:be0:0:0:0:44
ns3.satserver.nl. 5 AAAA 2a02:cc8:33:0:0:0:0:33
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0