The callee is busy at this location.
The callee is busy on all of their devices.
The destination could not be found.
The callee is temporarily unavailable.
The number was blocked by the dial-plan allowlist.
The call was blocked by the remote network.
The callee declined the call.
The call was rejected by the remote party as unwanted.
The server encountered an internal error.
The calling service is currently unavailable.
The media resource was reset.
The failure reason was not recognized.
SIP-level failure reason for a voice call.
Unrecognized server values map to UNKNOWN.