What is the most likely cause of this failure?

Refer to the exhibit.

A network engineer is attempting to register a Cisco TelePresence endpoint to a Cisco Expressway.

What is the most likely cause of this failure?
A . The endpoint does not have the proper port assignments configured for SIP signaling
B . The Cisco Expressway failed to bind to the LDAP server, which is where the lab local SIP domain is learned
C . The lab local SIP domain does not exist on the Cisco Expressway
D . The endpoint uses the TCP protocol and the Cisco Expressway is configured to allow only TLS for SIP registrations
E . The lab local SIP domain is not configured in the Cisco Expressway allow list for registration

Answer: C