I emailed Vonage support, they repsonded with: I checked into these and see that the inbound call is received our platform tries to download your NCCO from your answer URL: https://api.vapi.ai/vonage/inbound_call The download attempt hits a 400 error and we are unable to receive any valid call control objects to process the call from your answer URL. Can you please check on this answer URL for any issue? httpStatus\":400,\"errorReason\":\"NCCO download error: 400\