31480: Temporarily Unavailable

This means the callee is currently unavailable. In the Voice JavaScript SDK changelog, Twilio maps this to ClientErrors.TemporarilyUnavilable, and the error dictionary lists it as a Voice ERROR.

• The callee is temporarily unavailable and cannot accept the call.
• Your client cannot reach Twilio's signaling or media infrastructure because DNS, firewall, or edge configuration blocks the required connections. Voice SDKs require both signaling and media connectivity.
• Your network restricts UDP, and you have not provided ICE servers from Twilio Network Traversal Service to establish media connectivity over TURN.

• Retry the call after the callee is available again.
• Allow outgoing TCP and UDP traffic from your application to Twilio's signaling and media servers, and make sure your firewall allows return traffic.
• If UDP is restricted, use Twilio Network Traversal Service and pass the returned ice_servers or iceServers values to your Voice client.
• If you use a restrictive network, choose a specific edge location that matches your deployment so you only need to allow the relevant media server addresses.

• Error and Warning Dictionary
• Voice SDK Error Codes
• Voice SDKs Network Connectivity Requirements