Hello VAPI Support Team, We are currently facing a SIP call transfer issue when using the single prompt transfer call function with our Netgsm (Turkish phone provider) SIP trunk. When we perform a call transfer via Workflows, everything works correctly. A REFER message is sent to Netgsm, and the call is successfully transferred. However, when we try the same transfer from a single prompt, Netgsm only receives a BYE message instead of REFER, which causes the call to be dropped instead of being transferred. We already confirmed this with Netgsm support: Workflows → REFER sent → transfer works Single prompt → BYE sent → call terminated It seems like the single prompt transfer function does not generate the SIP REFER request, unlike the workflow transfer. I am using the same transfer_call tool in both workflow and single prompt but i cannot forward the call in single prompt assitant Could you please check this on your side and confirm whether this is a limitation or a configuration issue? If possible, we need the single prompt transfer to behave the same way as workflow transfers (sending REFER instead of BYE). Thanks for your support. Best regards, https://cdn.discordapp.com/attachments/1410187721640513586/1410187721900687440/image_1.png?ex=68b01b28&is=68aec9a8&hm=c2630c66d97f1b6625a23f682c96250ffeb512377bdc34159d38d3dcf81e3aa0& https://cdn.discordapp.com/attachments/1410187721640513586/1410187722596945974/image_3.png?ex=68b01b29&is=68aec9a9&hm=ac9d61cfbd19b91a6c8e53157e2f4e7072de3724c9fb909c418ef1cb8a154e83&

Hi Halil, could you please share a call id with the assistant and the transfer tool failing?

For example this one call_id: 7e258f98-e65c-4361-a010-dd8635c98a3d assistant_id: 342aa7b1-f81f-452e-843c-a1e56249d0b4 tool_id: 41cbd95e-7dd3-4169-84e8-1532f4b5c7f2

checking if this is resolved/solved for you?