# SIP REFER transfer via Telnyx inbound trunk — 603 Decline on all attempts

**URL:** <https://community.livekit.io/t/sip-refer-transfer-via-telnyx-inbound-trunk-603-decline-on-all-attempts/901>\
**Category:** Telephony\
**Tags:** sip-telnyx, sip-trunking\
**Created:** [April 17, 2026, 8:52pm UTC](https://community.livekit.io/t/sip-refer-transfer-via-telnyx-inbound-trunk-603-decline-on-all-attempts/901 "2026-04-17T20:52:22Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![Lorde\_M](https://sea1.discourse-cdn.com/flex001/user_avatar/community.livekit.io/lorde_m/32/1076_2.png) [@Lorde\_M](https://community.livekit.io/u/Lorde_M)\
**Post date:** [April 17, 2026, 8:52pm UTC](https://community.livekit.io/t/sip-refer-transfer-via-telnyx-inbound-trunk-603-decline-on-all-attempts/901/1 "2026-04-17T20:52:22Z")

</div>

Cold transfer the caller to a human agent (PSTN number) via SIP REFER when the user requests it. We call `transfer_sip_participant` from inside a `@function_tool`:

```python
job_ctx = get_job_context()
room = job_ctx.room

sip_participant = next(
    (p for p in room.remote_participants.values()
     if p.kind == rtc.ParticipantKind.PARTICIPANT_KIND_SIP),
    None
)

await job_ctx.api.sip.transfer_sip_participant(
    livekit_api.TransferSIPParticipantRequest(
        room_name=room.name,
        participant_identity=sip_participant.identity,
        transfer_to="sip:+16282606639@sip.telnyx.com",
        play_dialtone=True,
        headers={
            "Diversion": "<sip:+16187338098@sip.telnyx.com>",
            "X-Detected-Topic": "...",
        },
    )
)

```

**What happens:**

The agent confirms the transfer verbally, the tool is called, the call **disconnects immediately** — the caller hears silence and the room closes. No actual transfer to the target number occurs.

On the **Telnyx portal → Outbound Call Reports** we see **7 outbound call attempts** , all failing with **SIP 603 Decline**.

**Questions:**

1. Does the Telnyx FQDN connection that receives the SIP REFER need an outbound voice profile to route the transfer leg to PSTN? Or does Telnyx route it differently from a regular outbound call?

2. Should `transfer_to` use `tel:+16282606639` format instead of `sip:+16282606639@sip.telnyx.com`?

3. Is there anything specific that needs to be enabled on the **LiveKit SIP trunk** side (not just Telnyx) to allow REFER to pass through? We only have one trunk and one dispatch rule.

4. Has anyone successfully done a cold transfer to a PSTN number via Telnyx? What was the exact Telnyx configuration required?

Any help appreciated — we’ve been going in circles on this one.

---

<div class="post-metadata">

**Author:** ![CWilson](https://sea1.discourse-cdn.com/flex001/user_avatar/community.livekit.io/cwilson/32/135_2.png) [@CWilson](https://community.livekit.io/u/CWilson)\
**Post date:** [April 20, 2026, 2:39pm UTC](https://community.livekit.io/t/sip-refer-transfer-via-telnyx-inbound-trunk-603-decline-on-all-attempts/901/2 "2026-04-20T14:39:07Z")

</div>

Refer has to be enabled by Telnyx.