Apex domains cannot have CNAME records.
Question and response
Question
dig mercadolibre.io. NS
Answer
mercadolibre.io. 5 NS ns-13.awsdns-01.com.
mercadolibre.io. 5 NS ns-1805.awsdns-33.co.uk.
mercadolibre.io. 5 NS ns-1191.awsdns-20.org.
mercadolibre.io. 5 NS ns-646.awsdns-16.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0