What is the cause of this issue?

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.