Transfer a SIP call to an external SIP endpoint using the SIP REFER method.
Unlike transfer()
which transfers control within RELAY, refer() performs a SIP-level transfer
to an external endpoint.
This method emits calling.call.refer events. See Call Events for payload details.
The target SIP device for the REFER.
Device type. Typically "sip".
SIP parameters including uri (the SIP URI to refer to).
URL to receive REFER status webhooks.
Promise<Record<string, unknown>> — Server response confirming the refer operation.