Call Transfer Not Working

Hi Guys,
I'm trying to set up a call-transfer tool for my assistant. I have tried several things following other posts and answers but haven't had any luck. Details below.

Experience:
  • I call the assistant through mobile / web interface
  • Guide conversation to initialise a call transfer
  • Tool call happens (can see in the logs / transcript)
  • Call hangs up (both on mobile / and web).
    this is what it looks like when I call via mobile (see attachment 1) vs via web (see attachment 2).
My set up:

I have a call transfer tool configured, and the assistant is given access to this tool.

Configuration 1.

  • assistant bound to twilio imported number
  • forward to VAPI issued number (bound to a separate assistant) ❌
  • forward to Australian Mobile Number (human) ❌
Configuration 2.
  • Assistant bound to VAPI issued number
  • Forward to Twilio Number ❌
  • Forward to Aus Mobile ❌
The above have been tested with :
  • EC16 numbers vs sip transfers
  • Blind vs Warm transfers
The experience is still the same. No forwarding.

Appreciate your assistance here.
Screenshot_2025-10-10_at_9.49.06_am.png
Screenshot_2025-10-10_at_9.48.29_am.png
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