While troubleshooting a connectivity issue between Cisco Unified Communications Manager, Expressway-C, and Expressway-E,

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While troubleshooting a connectivity issue between Cisco Unified Communications Manager, Expressway-C, and Expressway-E, an engineer sees this output in the Expressway-E logs:
Event="Authentication Failed" Service="SIP" Src-ip="10.50.2.1"
Src-port="25723" Detail="Incorrect authentication credential for user"
Protocol "TLS" Method="OPTIONS" Level="1"
What is the cause of this issue?

A. The Expressway-C Traversal Server username/password do not match the Expressway-E Traversal Zone username/password.
B. The Expressway-C Traversal Client username/password do not match the Expressway-E Traversal Server username/password.
C. The Expressway-C Traversal Zone username/password do not match the Expressway-E Traversal Zone username/password.
D. The Expressway-C Traversal Zone username/password do not match the Expressway-E Traversal Client username/password.
E. The Expressway-C Traversal Server username/password do not match the Expressway-E Traversal Client username/password.