Hi all, this is my first time posting here, thanks in advance for your help! I’m having issues with the Slack Trigger node in n8n, Slack cannot verify the URL, and the request gets blocked by n8n, even though the workflow is active and all environment variables are correctly set.
The Problem
Slack fails to verify the trigger URL, and the n8n logs show:
Blocked POST /webhook/xxxxx/webhook for “Slackbot 1.0 (+https://api.slack.com/robots)”
Even though:
• Slack Trigger workflow is active
• Env var N8N_BLOCK_WEBHOOKS_WITHOUT_USER_AGENT is set to false
• No reverse proxy other than Cloudflare
• Tested on both 1.109.2 and 1.110.1 — same issue
• Test URL works (via Slack Trigger “Test Event” in n8n), but Production URL doesn’t
Tried So Far
• Manually confirmed all environment variables in container
• Tried both old and new Slack triggers
• Restarted Docker, rebuilt container
• Cloudflare rules: none blocking these requests
• Cannot disable Cloudflare proxy (Free plan)
• Cannot use Workers Rewrite (Free plan limitations)
Anyone know anything about this? Thanks a lot!!
My Set Up
• n8n version: 1.110.1
• Database: Postgres
• n8n EXECUTIONS_PROCESS: main
• Running via: Docker
• Operating system: Ubuntu (Oracle Cloud VM)
• Reverse proxy: only Cloudflare (proxied, Free plan)
• Docker env includes:
N8N_BLOCK_WEBHOOKS_WITHOUT_USER_AGENT=false
N8N_TRUSTED_PROXIES=*
N8N_RATE_LIMIT_DISABLED=true
WEBHOOK_URL, N8N_PUBLIC_URL, N8N_EDITOR_BASE_URL all set correctly