Hi Sid,
Thank you for the detailed report — this is really helpful. I've reviewed the failing call IDs and can confirm that the error is occurring at the transport layer, before any telephony provider is even reached. Since this is happening across Vapi numbers, Twilio, and Telnyx (including a blank assistant test), this points to an org-level provisioning issue on our side rather than anything in your configuration.
I've escalated this directly to our engineering team with your orgId and call IDs, with a request to check and reset outbound transport provisioning for your account.
You don't need to make any changes on your end. I'll follow up as soon as I have an update from the team — we're treating this as high priority.
Apologies for the disruption and thanks for your patience!