A Cisco TelePresence EX Series desktop endpoint failed to register to a Cisco VCS. The SIP status shows "Failed: 403 Forbidden" in the endpoint's web interface. What is the first thing that should be

In SIP signaling, a 403 Forbidden status code means the server received a valid request but is denying it due to an authorization failure. On a Cisco VCS, this typically occurs when the endpoint's configured SIP username or password does not match what is provisioned on the VCS or the authentication server. Verifying and correcting the SIP authentication credentials in the endpoint's configuration is the appropriate first troubleshooting step.

CallSetup Mode should be set to Direct for SIP registrations to a VCS, not Gatekeeper, which is used for H.323; additionally, this setting would produce a different error than 403 Forbidden.

Outbound Connection Credentials relate to traversal or B2B authentication scenarios and would not typically cause a 403 Forbidden on a standard internal VCS registration.

If SIP Mode were Off the endpoint would not attempt SIP registration at all and no 403 response would be generated, making this an unlikely root cause.