### Answer This appears to be a known issue with Multi-Prompt Agents. [(1) ]() Another user reported the same behavior where custom SIP headers added to the

call_transfer

function do not persist—the headers appear empty when re-entering the function, and call logs show

custom sip headers undefined

. This seems to be a UI/saving bug rather than a configuration error on your part. I'd recommend reaching out to Retell support directly to report this issue and get a timeline for a fix. In the meantime, you could try: - Using a Conversation Flow agent instead, which has a Call Transfer Node that also supports custom SIP headers [(2) ]() - Checking if the issue persists after refreshing or re-creating the transfer call tool

​ To learn more, see the sources I considered: [[1] Call_transfer - Custom SIP headers not saving on Multi_Prompt Agent](https://discord.com/channels/1186424376300679209/1430166790079516762) [[2] Call Transfer Node](https://docs.retellai.com/build/conversation-flow/call-transfer-node) ​

Feel free to tag @AI Evy with additional questions. I also appreciate feedback, it helps me improve.