Slack Trigger/Webhook URLs Won't Verify - Production URL Fails, Only Test URL Works

Questions
1

Hi n8n Community,

I’m struggling with a Slack integration where webhook URLs won’t verify properly, preventing workflow activation.

Setup:

  • Instance: n8n Cloud (eric0007.app.n8n.cloud)

  • Plan: Starter

  • Workflow: Slack bot integration (Natasha Main)

  • Issue: Cannot activate any workflow with webhook triggers

The Problem:

When setting up Slack Event Subscriptions:

  • :white_check_mark: Test URL verifies: https://eric0007.app.n8n.cloud/webhook-test/[id]/webhook

  • :cross_mark: Production URL fails: https://eric0007.app.n8n.cloud/webhook/[id]/webhook

Error from Slack: “Your request URL responded with an HTTP error”

What I’ve Tried:

With Slack Trigger Node:

  1. Created Slack app with proper OAuth scopes

  2. Added signing secret to n8n credentials

  3. Configured Event Subscriptions with both message.channels and app_mention

  4. Test URL verifies when workflow is inactive

  5. Production URL fails when trying to activate workflow

  6. Get error: “Problem activating workflow - Please resolve outstanding issues”

With Generic Webhook Node:

  1. Created simple webhook (Path: slack-natasha, Method: POST, Respond: Immediately)

  2. Same issue - Production URL doesn’t verify in Slack

  3. Cannot activate workflow

Observations:

  • The Test URL path (/webhook-test/) works fine for verification

  • The Production URL path (/webhook/) always fails Slack’s challenge

  • When workflow is Active, n8n listens on Production URL

  • When workflow is Inactive, n8n responds on Test URL

  • This creates a catch-22: Slack won’t verify Production URL, but workflow needs to be active to listen on it

Questions:

  1. Is there a known issue with Slack webhook verification on n8n Cloud Starter plan?

  2. Should Production URLs be able to verify in Slack Event Subscriptions?

  3. Is there a configuration I’m missing to make Production webhooks work?

  4. Do I need to upgrade to a different plan for Slack webhooks to work properly?

Any guidance would be greatly appreciated! This is blocking my entire Slack integration project.

n8n Version: Cloud (latest)
Node Versions: Slack Trigger v1, Webhook v1

Describe the problem/error/question

What is the error message (if any)?

Please share your workflow

(Select the nodes on your canvas and use the keyboard shortcuts CMD+C/CTRL+C and CMD+V/CTRL+V to copy and paste the workflow.)

Share the output returned by the last node

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:
2

Try using a regular Webhook node (not Slack Trigger) that can handle Slack’s verification:

  1. Delete the Slack Trigger node

  2. Add a Webhook node:

    • Path: slack-webhook (or whatever you want)

    • Method: POST

    • Respond: Immediately

    • Response Code: 200

  3. Add a Code node connected to the Webhook:

javascript

   if (items[0].json.body.challenge) {
     return [{
       json: {
         challenge: items[0].json.body.challenge
       }
     }];
   }
   return items;

  1. Activate this workflow

  2. Copy the production URL and paste it in Slack’s Event Subscriptions

It should verify now. After that, you can add your actual Slack bot logic to the workflow.