Apex domains cannot have CNAME records.
Question and response
Question
dig mercadolibre.com. NS
Answer
mercadolibre.com. 5 NS ns-1708.awsdns-21.co.uk.
mercadolibre.com. 5 NS ns-1451.awsdns-53.org.
mercadolibre.com. 5 NS ns-368.awsdns-46.com.
mercadolibre.com. 5 NS ns-984.awsdns-59.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0