Hi all, I need help with Slack Events API verification.
Environment
• n8n: 1.116.2 (Self-Hosted)
• Docker + Postgres backend
• Reverse Proxy: Caddy v2.10.2
• Host: Ubuntu 22.04 LTS
• WEBHOOK_URL + N8N_HOST + N8N_PROTOCOL set correctly
• N8N_TRUST_PROXY=true
Slack Setup
• Request URL:
https://n8n.hansei.pro/webhook/slack-events
• Event: url_verification
• Method: POST
Workflow
• Webhook node (POST, respond via Respond to Webhook)
• IF → Respond to Webhook (text body = challenge string)
• Workflow is Active with green dot
Symptoms
• GET returns correct 404: webhook not registered for GET
• Webhook is reachable via browser
• But POST returns:
{“code”:0,“message”:“Workflow Webhook Error: Workflow could not be started!”}
• Same result using curl test payload:
-d ‘{“type”:“url_verification”,“challenge”:“abc123”}’
• No webhook-related logs appear in docker logs n8n
Goal
Slack URL Verification should return raw challenge string (e.g. “abc123”) and show 
Verified in Slack.
What I suspect
Webhook endpoint is not fully registered in the execution engine. Maybe something with proxy headers / webhook registry.
Any insight appreciated. Thank you! find solutions is by using the 
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Information on your n8n setup
- n8n version:
- Database (default: SQLite):
- n8n EXECUTIONS_PROCESS setting (default: own, main):
- Running n8n via (Docker, npm, n8n cloud, desktop app):
- Operating system: