Build an Automated Financial Controller with n8n

What We'll Build

By the end of this tutorial, you'll have an n8n workflow that:

• Monitors an email inbox ([email protected]) in real-time
• Detects invoices in attachments (PDF, images)
• Automatically extracts key data: supplier, net amount, VAT, date, invoice number
• Files and archives invoices in Google Drive or your storage
• Updates a tracking sheet (Google Sheets, Airtable, or your ERP)
• Alerts your team for invoices requiring manual validation

Workflow Architecture

Here's the complete workflow diagram:

┌─────────────┐    ┌──────────────┐    ┌─────────────────┐
│   Email     │───▶│  Invoice     │───▶│   Attachment    │
│  (Trigger)  │    │  Filtering   │    │   Extraction    │
└─────────────┘    └──────────────┘    └─────────────────┘
                                              │
                                              ▼
┌─────────────┐    ┌──────────────┐    ┌─────────────────┐
│   Slack     │◀───│    Data      │◀───│   OCR / AI      │
│   Alert     │    │  Validation  │    │   Extraction    │
└─────────────┘    └──────────────┘    └─────────────────┘
                          │
                          ▼
              ┌──────────────────────┐
              │   Storage & Export   │
              │  (Drive + Sheets)    │
              └──────────────────────┘
    

Step 1: Configure the Email Trigger

Start by creating a new workflow in n8n and add an Email Trigger (IMAP) or Gmail Trigger node depending on your provider.

Gmail Configuration

Pro Tip: Create a dedicated email address (invoices@...) and ask your suppliers to send invoices there. This simplifies filtering.

Step 2: Filter Emails Containing Invoices

Not all emails with PDFs are invoices. Add an IF node to filter:

// IF node condition
{{ $json.subject.toLowerCase().includes('invoice')
   || $json.subject.toLowerCase().includes('bill')
   || $json.from.email.includes('accounting')
   || $json.from.email.includes('billing') }}
    

Step 3: Extract Data with AI

This is the magic part. We'll use AI (GPT-4 or Claude) to extract structured information from the invoice.

Option A: Extraction via OpenAI Vision

If your invoices are images or scanned PDFs, use GPT-4 Vision:

// OpenAI node settings
Model: gpt-4-vision-preview
Message:
"Analyze this invoice and extract the following information as JSON:
- supplier_name
- invoice_number
- invoice_date (format YYYY-MM-DD)
- net_amount
- vat
- total_amount
- currency

Reply ONLY with the JSON, no comments."
    

Option B: Extraction via Claude (Anthropic)

Claude excels at structured extraction. Use the HTTP Request node:

// HTTP Request to Claude API
POST https://api.anthropic.com/v1/messages
Headers:
  x-api-key: YOUR_API_KEY
  anthropic-version: 2023-06-01

Body:
{
  "model": "claude-3-5-sonnet-20241022",
  "max_tokens": 1024,
  "messages": [{
    "role": "user",
    "content": [
      {"type": "image", "source": {"type": "base64", "data": "{{$binary.data}}"}},
      {"type": "text", "text": "Extract data from this invoice as JSON..."}
    ]
  }]
}
    

Step 4: Validate and Clean Data

AI can sometimes make mistakes. Add a Code node to validate:

// Code node - Validate extracted data
const data = $input.first().json;

// Parse AI JSON
let invoice;
try {
  invoice = JSON.parse(data.content);
} catch (e) {
  return { error: "Invalid JSON", raw: data.content };
}

// Validation
const isValid =
  invoice.total_amount > 0 &&
  invoice.invoice_date.match(/\d{4}-\d{2}-\d{2}/) &&
  invoice.supplier_name.length > 2;

return {
  ...invoice,
  validation_status: isValid ? "OK" : "REVIEW_NEEDED",
  processed_at: new Date().toISOString()
};
    

Step 5: Archive in Google Drive

Create an organized folder structure by year/month/supplier:

Invoices/
├── 2026/
│   ├── 01-January/
│   │   ├── Amazon/
│   │   ├── AWS/
│   │   └── ...
│   ├── 02-February/
│   └── ...
└── TO_REVIEW/
    

Expected Results

Going Further

This basic workflow can be extended with:

• ERP Integration: Automatic sending to Sage, Odoo, or QuickBooks
• Duplicate Detection: Check if invoice already exists
• Bank Reconciliation: Link with bank transactions
• Automated Reporting: Monthly expense dashboard by supplier
• Approval Workflow: Multi-level validation circuit

Conclusion

With n8n and AI, you can transform supplier invoice management from a manual chore into a fully automated process. The "automated financial controller" never sleeps, doesn't make data entry errors, and alerts you only when necessary.

That's intelligent automation serving SMEs.