Apex domains cannot have CNAME records.
Question and response
Question
dig mz. NS
Answer
mz. 5 NS phloem.uoregon.edu.
mz. 5 NS ns-mz.afrinic.net.
mz. 5 NS zebra.uem.mz.
mz. 5 NS anyns.uem.mz.
mz. 5 NS dzowo.uem.mz.
mz. 5 NS oceano.uem.mz.
Authority
The response has no authority records.
Additional
anyns.uem.mz. 151644 A 204.61.216.14
dzowo.uem.mz. 151677 A 196.3.96.66
zebra.uem.mz. 112448 A 196.3.96.67
oceano.uem.mz. 151677 A 196.3.96.69
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0