Vapi Tool Call (Sync) Logs "No result returned." Despite Successful n8n Webhook Response (200 OK + J
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!
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!
