Apex domains cannot have CNAME records.
Question and response
Question
dig agps-poitoucharentes.com. NS
Answer
agps-poitoucharentes.com. 5 NS ns2.agps-poitoucharentes.com.
agps-poitoucharentes.com. 5 NS ns1.agps-poitoucharentes.com.
Authority
The response has no authority records.
Additional
ns1.agps-poitoucharentes.com. 5 A 62.171.142.121
ns2.agps-poitoucharentes.com. 5 A 62.169.19.112
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0