| name | vapi-voice |
| description | How to set up and trigger the live AI-vs-AI phone negotiation with Vapi (or Retell/Bland) - two assistants, an outbound call, and transcript streaming into run state. Use for the voice close. |
Vapi Voice (AI-vs-AI live call)
The WOW moment: the procurement assistant phones the supplier assistant and they negotiate live,
with the transcript streaming to the dashboard.
Setup (once)
- Supplier assistant (inbound): a Vapi assistant whose system prompt = the
supplier-simulator
persona + hidden floor. Attach to a phone number.
- Procurement assistant (outbound): a Vapi assistant whose system prompt = buyer negotiator
using the
negotiation-playbook, with dynamic variables for product, quantity, currentPrice,
target, walkAway.
- Webhook: point Vapi server messages (transcript, end-of-call-report) at your Next.js route
/api/vapi/webhook, which appends rounds to state/run-<id>.json.
Trigger an outbound call
curl -X POST https://api.vapi.ai/call \
-H "Authorization: Bearer $VAPI_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"assistantId": "<procurement_assistant_id>",
"phoneNumberId": "<your_vapi_number_id>",
"customer": { "number": "<supplier_assistant_number>" },
"assistantOverrides": {
"variableValues": { "product": "office chairs", "quantity": 500,
"currentPrice": 80, "target": 74, "walkAway": 80 }
}
}'
Capture results
On end-of-call-report, parse the transcript for the final agreed price and terms; write a
channel: "voice" round + voiceFinalPrice to state; hand to quote-analyst.
Demo tips
- Keep it < 90s: prompt both assistants to be decisive.
- Have the procurement assistant restate final terms aloud before hangup (clean extraction + great TV).
- Fallback: pre-record one good call transcript; if the live call errors, replay it through the
same UI path so the dashboard still completes. Log that fallback was used.
- Alternatives with the same pattern: Retell, Bland.
