Apex domains cannot have CNAME records.
Question and response
Question
dig braintreegateway.com. NS
Answer
braintreegateway.com. 5 NS pdns100.ultradns.net.
braintreegateway.com. 5 NS ns1-pchnet.paypal.com.
braintreegateway.com. 5 NS ns2-pchnet.paypal.com.
braintreegateway.com. 5 NS pdns100.ultradns.com.
Authority
The response has no authority records.
Additional
ns1-pchnet.paypal.com. 5 A 64.78.206.1
ns2-pchnet.paypal.com. 5 A 64.78.207.1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0