Hello, We need help configuring call transfer using SIP REFER in Retell AI. Current Topology Call flow: Call enters our PBX. The PBX IVR answers the call. When the caller presses option 1, the call is transferred to Retell AI. Retell AI identifies the state/city (for example: State 1 o…

Based on your topology where calls enter your PBX first and then dial into Retell AI, you’re using the “Dial to SIP URI” method (1) . This integration method has a critical limitation for call transfers. SIP REFER Support Status The “Dial to SIP URI” method does not support Retell’s built-in transfer…

Hello, Thank you for the clarification. We will proceed with Option 2 and implement the transfer logic on our PBX side. We understand that when using “Dial to SIP URI”, SIP REFER is not supported. Therefore, instead of transferring the active dialog, Retell will initiate a new outbound SIP call t…

Please provide the official outbound SIP IP address range to be whitelisted on our firewall.

Hello @suporte Please check this guide : Custom Telephony Overview - Retell AI

Transfer call using SIP REFER to different destinations based on detected intent/state

Support Help

Omar_Ashraf March 3, 2026, 9:43pm 4

Hello @suporte,

Yes, dynamic transfer destination is supported.

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Transfer call using SIP REFER to different destinations based on detected intent/state

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