We’re using a Twilio number with Vapi transferCall and warm-transfer-experimental. Twilio’s docs say original caller ID can be preserved on forwarded calls if the inbound CallToken is passed to the forwarded leg. Does Vapi’s transferCall implementation pass that CallToken or otherwise preserve the original caller ID when transferring to an external PSTN destination? Right now the destination system is seeing the Vapi/Twilio number instead of the original caller’s number.

No right now Vapi’s transferCall (including warm-transfer-experimental) doesn’t reliably pass the Twilio CallToken or preserve the original caller ID on the forwarded leg. That’s why the destination is seeing the Vapi/Twilio number instead of the caller’s number. This is more of a platform limitation than a config issue. I can help you validate it with a quick call trace and confirm exactly where the caller ID is getting lost if you want. @nightcrawler

Hi, Thank you for reaching out. Vapi's transferCall does preserve the CallToken For the

callToken

to be preserved, all of the following conditions must be met: 1. The transfer must use

warm-transfer-experimental

mode 2. No explicit

callerId

override should be set on the destination 3. The call transport must be Twilio with a valid

callToken

(for example, an inbound Twilio Verified Call)