SIP
480 Temporarily Unavailable
The callee's end system was contacted successfully but the callee is currently unavailable. The client may retry after some time.
Когда вы видите этот код
When the user exists but is not currently reachable — phone is off, DND mode enabled, or all lines are busy.
Как исправить
Try calling again later. Check if the callee has DND enabled or if their device is powered off. Configure voicemail for unavailable scenarios.