Hey Vapi Team/Community! 👋 Struggling with a sync tool call (get_available_slots, ID: da4ab4a8-6750-40ba-844d-7a8aa6e0005f) that connects to an n8n webhook. Problem: During live calls, Vapi logs "result": "No result returned." for this tool call. Consequently, the AI doesn't get the {{response.*}} data and hallucinates (e.g., invents random dates). Key Evidence: ✅ Vapi "Test Tool" Button: WORKS PERFECTLY! Shows 200 OK and the correct JSON response body from n8n. ✅ n8n Execution Logs: Show the webhook receiving the call and the workflow completing successfully, returning a 200 OK with the correct JSON body. ❌ Vapi Live Call Logs: Still show "result": "No result returned." for the exact same tool call ID during the conversation flow. Setup & Troubleshooting Done: Tool Async: OFF (confirmed & saved multiple times). Tool Timeout: 60s. n8n webhook is Active and URL matches Vapi Tool Server URL. n8n returns correct JSON structure (snake_case) with Content-Type: application/json header. SSML script uses matching {{response.snake_case_variable}}. AI Prompt/Hard Rules instruct strongly to use response data. Self-hosted n8n on Railway (logs checked, no obvious errors there). Question: Why would Vapi fail to register the result during a live call when the backend (n8n) demonstrably sends a valid 200 OK + JSON response, and the same call works perfectly via the "Test Tool" button? Is this a known Vapi behavior, a parsing issue, or something else I can check? Thanks for any pointers! 🙏

Try using the webhook to respond directly instead of using the Vapi module. According to a user with a similar issue:

json
// Ensure your response includes the exact toolCallId from the request
{
  "toolCallId": "call_EXACT_ID_FROM_REQUEST",
  "result": "Your result data here"
}

Make sure the

toolCallId

in your response exactly matches the ID sent by Vapi in the initial request, as mismatched IDs are a common cause of "No result returned" errors. Sources: - [Discord discussion about webhook response workaround](https://discord.com/channels/1211482211119796234/1334661059298066514) - [Discord discussion about toolCallId matching](https://discord.com/channels/1211482211119796234/1325000684231196775)

Hey! To help track down this issue, could you share: - The call ID - When exactly this happened (the timestamp) - What response you expected to get - What response you actually got instead This would really help us figure out what went wrong!

I've identified the key issue! The response format from n8n doesn't match what VAPI expects. VAPI expects webhooks to return a response with: \-

toolCallId

(camelCase) \-

result

field containing the data But your n8n response is using: \-

tool_call_id

(snake_case) \- Everything else looks correct This naming mismatch is why VAPI can't process the response properly. When VAPI checks for a matching toolCallId, it can't find it because n8n is returning

tool_call_id

instead. Change your n8n "Respond to Webhook" node to return this exact format: \`\`\`json { "toolCallId": "call_JHJWNDzOB5XPHFGuwguV5lLR", "result": "{"no_slots_found":false,"morning_day_1":"lunedì 12 maggio","morning_hour_1":"10:00","slot_1_iso":"2025-05-12T10:00:00+02:00","only_one_slot_found":true}" } \`\`\` This camelCase field naming is critical - VAPI strictly checks for

toolCallId

(not

tool_call_id

), and if it doesn't find it, returns the "No result returned" error.