Thank you for your detailed description. To help troubleshoot, could you confirm which telephony provider (e.g., Twilio, Telnyx) you are using for the call transfer, and whether the number you are trying to use as the caller ID is verified with that provider? This will help determine if the issue is related to provider restrictions or configuration.
Sources:
- [Vapi documentation: call forwarding](
https://docs.vapi.ai/call-forwarding)
- [Vapi SIP Trunking Telnyx external number call forwarding troubleshooting](
https://discord.com/channels/1211482211119796234/1343963959421829172)