Automatically Validate and Archive E-Invoices with n8n

You receive e-invoices every day via email – as XML attachments, ZUGFeRD PDFs, or in Peppol format. Each one needs to be checked, classified, and stored in a legally compliant manner. Doing this manually doesn't just take time – it's also error-prone.

In this tutorial, we'll build a complete n8n workflow that automatically detects, validates, and archives incoming e-invoices – and fires a Slack alert the moment something goes wrong.

Looking for n8n basics? Check out our complete n8n documentation – with installation guide, code examples, and ready-made workflow templates.

The Problem: Manual Invoice Checking Doesn't Scale

In many companies, the process looks like this today:

1. An employee opens an email with an invoice attachment
2. Downloads the file and manually identifies the format
3. Uploads it to a validation tool and checks the result
4. Contacts the supplier if there are errors
5. Files valid invoices in the correct folder

With 5 invoices a day, that's manageable. With 50 or 500, it becomes a bottleneck – and every missed error can cause problems during a tax audit.

Workflow Overview

Our automated workflow consists of 6 steps:

1Email (IMAP) → Parse Auto-Detect → Validate → IF Branch
2                                                 ├─ Success → Google Drive Upload
3                                                 └─ Error → Slack Alert

What the workflow does:

• Automatic format detection – XRechnung, ZUGFeRD, Factur-X, UBL, or CII is detected automatically
• Schema and business rule validation – Checks against official Schematron rules
• Archiving – Valid invoices are automatically uploaded to Google Drive
• Error escalation – Invalid invoices trigger a Slack alert with specific error codes

Step 1: IMAP Trigger – Receive Emails with Invoices

Create a new workflow in n8n and add an IMAP Email Trigger as the first node.

Configuration:

The node watches your mailbox and triggers the workflow whenever a new email with an attachment arrives. Attachments are passed along as binary data.

Tip: Create a mail filter rule that automatically moves invoices to a subfolder like Invoices. Then point the IMAP trigger specifically at that folder.

Step 2: Parse with Auto-Detect – Automatically Identify the Format

Add an HTTP Request node that sends the invoice to the Invoice-api.xhub Parse API – with automatic format detection.

HTTP Request Configuration:

1Method: POST
2URL: https://service.invoice-api.xhub.io/api/v1/invoice/parse
3Authentication: Header Auth
4  Header Name: x-api-key
5  Header Value: {{ $credentials.invoiceApiKey }}
6Body Type: Binary
7Content Type: auto
8Send Binary Data: enabled

The API automatically detects whether the file is an XRechnung (UBL/CII), ZUGFeRD, Factur-X, or another format. The response includes a detection object:

1{
2  "detection": {
3    "format": "XRechnung",
4    "formatVersion": "3.0.2",
5    "syntax": "CII",
6    "countryCode": "DE",
7    "confidence": 98,
8    "formatMethod": "schemaAnalysis"
9  },
10  "invoice": {
11    "invoiceNumber": "INV-2026-001",
12    "issueDate": "2026-05-01",
13    "seller": {
14      "name": "Sample Supplier GmbH",
15      "vatId": "DE123456789"
16    },
17    "buyer": {
18      "name": "Your Company GmbH"
19    },
20    "countrySpecific": {
21      "countryCode": "DE",
22      "leitwegId": "991-12345-67"
23    },
24    "total": 1190.00,
25    "currency": "EUR"
26  }
27}

Key fields in the detection object:

More on the API: Find the full reference in the n8n integration documentation.

Step 3: Validate – Check the Invoice Against Official Rules

Add another HTTP Request node that validates the parsed invoice:

1Method: POST
2URL: https://service.invoice-api.xhub.io/api/v1/invoice/de/validate
3Authentication: Header Auth
4  Header Name: x-api-key
5  Header Value: {{ $credentials.invoiceApiKey }}
6Body Type: Binary
7Send Binary Data: enabled

The Validate API checks the invoice against:

• Schema validation – Does the XML structure conform to the standard?
• Schematron business rules – Are all required fields present? Do the calculations add up?
• Country-specific rules – DE: XRechnung conformity, Leitweg-ID, etc.

The response contains the validation status:

1{
2  "valid": false,
3  "errors": [
4    {
5      "code": "BR-DE-01",
6      "severity": "error",
7      "message": "An invoice (BG-0) must contain a Buyer reference (BT-10).",
8      "location": "/Invoice/cac:AccountingCustomerParty"
9    }
10  ],
11  "warnings": [
12    {
13      "code": "BR-DE-15",
14      "severity": "warning",
15      "message": "The element 'Payment terms' (BT-20) should be provided."
16    }
17  ]
18}

Step 4: IF Branch – Success or Error

Add an IF node to branch the workflow based on the validation result:

Condition:

1{{ $json.valid }} equals true

Success: Google Drive Upload

When the invoice is valid, it gets automatically archived to Google Drive.

Add a Google Drive node:

Invoices are automatically sorted into monthly folders – perfect for compliant archiving.

Error: Slack Alert

When validation fails, a Slack alert is sent.

Add a Slack node:

Message:

1:warning: Invalid e-invoice detected!
2 
3Invoice: {{ $json.invoice.invoiceNumber }}
4Supplier: {{ $json.invoice.seller.name }}
5Format: {{ $json.detection.format }}
6 
7Errors:
8{{ $json.errors.map(e => `• [${e.code}] ${e.message}`).join('\n') }}
9 
10Please review manually.

This ensures the responsible team is notified immediately – with all relevant details and specific error codes.

Common Validation Errors

These errors come up most frequently in practice:

Tip: Use the error code as a search term in the n8n integration docs to find specific solutions.

Download the Workflow Template

You can download the complete workflow as a JSON template and import it directly into n8n:

Download workflow template

Import via Settings → Import Workflow in your n8n instance. You only need to add your API credentials and Slack/Google Drive connections.

Extension Ideas

The base workflow can be extended in many ways:

DATEV Export

Add another HTTP Request node after successful validation that converts the invoice to DATEV format via the Invoice-api.xhub API. This way, validated invoices automatically flow into your accounting system.

Duplicate Detection

Store invoice numbers and supplier IDs in a database (e.g., Airtable or PostgreSQL). Before archiving, use an IF node to check whether an invoice with the same number already exists – preventing duplicate bookings.

PDF Preview Generation

Use the Generate API from Invoice-api.xhub to automatically create a PDF preview from the validated XML invoice. This can be archived alongside the XML file – handy for team members who can't read XML.

Confidence-Based Routing

Use the confidence field from the auto-detection: if the value is below 90, route the invoice for manual review instead of processing it automatically.

Conclusion

With n8n and Invoice-api.xhub, you can automate the entire incoming invoice process – from email to archive. The workflow:

• Detects the invoice format automatically
• Validates against official standards and business rules
• Archives valid invoices in a compliant manner
• Escalates errors immediately to the responsible team

The best part: you don't need to write a single line of code. The entire logic is built visually in n8n.

Ready to get started?

1. Get a free API key
2. Read the n8n integration documentation
3. Import the workflow template