Warm transfer outbound consult INVITE is canceled and retried, causing 482 Request merged

[Bolu-Rio-Eigen]

We’re seeing a warm transfer failure with LiveKit SIP and I think the problem is happening in the SIP server layer, not the app.

Setup:

• provider: Africa’s Talking
• transport: UDP
• deployment: EC2
• livekit/sip version from logs: v2.11.4-0.20251016050252-63f7c8381817

Flow:

• inbound PSTN/SIP call comes into LiveKit SIP
• during the active call, we create an outbound consult leg with CreateSIPParticipant into a consultation room

What I expected:

• one outbound INVITE for the consult leg
• then either answer / reject / timeout from the provider

What is actually happening:

• LiveKit SIP sends the first outbound INVITE
• then sends CANCEL for that INVITE
• provider responds 487 Request Terminated
• LiveKit SIP then sends a second INVITE
• provider responds 482 Request merged

From pcap:

• 08:42:33.998765 first outbound INVITE
• 08:42:36.411865 CANCEL from our side
• 08:42:36.536778 487 Request Terminated
• 08:42:36.723757 second outbound INVITE
• 08:42:36.848409 482 Request merged

From SIP server logs:

• SIP invite failed ... error: "canceled"
• then another Creating SIP participant
• then SIP invite failed ... error: "unexpected status from INVITE response: sip status: 482: Request merged"

I don’t see this second attempt being intentionally triggered from app logic, so I’m trying to understand:

• what causes the first outbound INVITE to get canceled?
• why does a second INVITE get sent immediately after?
• is this expected behavior in livekit/sip warm transfer / CreateSIPParticipant flow?

Happy to attach the pcap and full logs if useful.