When using Slack interactive approval buttons with the Slack Send Message and Wait for Response node (or when using Webhook-waiting URLs), clicking the button from Slack often results in:
Browser/UI:
Invalid token
n8n logs:
Received request for unknown webhook:
The requested webhook "<uuid>/webhook" is not registered.
This happens even though:
Workflow is active
Slack message was generated by the same node
The webhook was registered properly before
Root Cause (Observed)
The webhook URLs used by the “Wait for response” Slack node:
/webhook-waiting/<node-uuid>
are temporary and become invalid if:
Workflow is briefly deactivated and reactivated
n8n container restarts (Kubernetes rollout)
n8n reloads workflows after update
Scaling or leader election changes webhook registration state
Slack continues sending requests to the old webhook-waiting URL embedded in the original message, which n8n no longer recognizes. so the error is thrown.
This causes broken approval flows in production.
Steps to Reproduce
Create workflow with Slack “Send Message and Wait for Response”
Activate and send approval message → Works
Restart n8n pod (Kubernetes) or deactivate/activate workflow
Click Approve/Reject on original Slack message
→ Invalid token + unknown webhook
Environment
-
n8n: 1.116.2
-
Deployment: Self-hosted Kubernetes
-
TLS termination via Ingress
-
Slack App: Interactivity & Shortcuts enabled