Log invoice approval decisions from Slack to Google Sheets

Description

What This Workflow Does
Listens for button clicks from the Invoice → Slack Approval workflow. When someone clicks Approve, Reject, or Flag on an invoice in Slack, this workflow captures that decision, logs it to Google Sheets, and sends a confirmation notification.

How It Works
Webhook Trigger – Receives POST request from Slack when a button is clicked
Parse Payload – Extracts the JSON payload from Slack's request body
Extract Decision Data – Pulls decision, user info, and invoice details from the message
Route by Decision – Branches to Approved, Rejected, or Flagged path
Log to Sheets – Appends invoice data to the appropriate sheet tab
Notify via Slack – Sends confirmation DM to the approver

Decision Routes
✅ Approved → Logs to "Approved" sheet → DM confirmation
❌ Rejected → Logs to "Rejected" sheet → DM confirmation
🚩 Flagged → Logs to "Flagged" sheet → DM for manual review

Setup Guide

1. Create Google Sheet
Create a new Google Sheet with 3 tabs: Approved, Rejected, Flagged
Add these column headers to each tab:
Supplier Name
Invoice Number
Amount
Date
Copy the Sheet ID from the URL

2. Connect the Nodes in n8n
Add your Google Sheets OAuth2 credential to all three logging nodes
Update the Document ID in each Google Sheets node to your Sheet ID
Add your Slack API credential to all three notification nodes
Update the User ID in the notification nodes (or change to channel)

3. Configure Slack Interactivity
Go to api.slack.com/apps → your app → Interactivity & Shortcuts
Set the Request URL to this workflow's webhook URL
Save Changes

4. Activate & Test
Click Active in the top-right corner of n8n
Trigger the Invoice Approval workflow to send a Slack message
Click a button in Slack
Check Google Sheets and Slack for results