Apex domains cannot have CNAME records.
Question and response
Question
dig curso-de-guitarra.com. NS
Answer
curso-de-guitarra.com. 5 NS ns-1040.awsdns-02.org.
curso-de-guitarra.com. 5 NS ns-493.awsdns-61.com.
curso-de-guitarra.com. 5 NS ns-1209.awsdns-23.org.
curso-de-guitarra.com. 5 NS ns-1154.awsdns-16.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0