Validation During Development

Overview

The /api/validate/json endpoint is essential for development. It validates your invoice JSON and ensures it can be converted to valid UBL BIS Billing 3.0 format before you create any documents.

You cannot create documents with invalid JSON. The API will reject invoices that don’t meet UBL BIS Billing 3.0 standards. Always validate during development to catch errors early.

Why Validate?

No document creation: Validation doesn’t create any records - it’s risk-free testing
Fast feedback: Get instant validation results without creating documents
Detailed errors: Receive specific field-level error messages
UBL compliance: Ensures your JSON converts to valid UBL BIS Billing 3.0 XML
Save API calls: Fix errors before attempting to create documents

Basic Validation

Use POST /api/validate/json with your invoice data:

curl -X POST "https://api.e-invoice.be/api/validate/json" \
     -H "Authorization: Bearer YOUR_API_KEY" \
     -H "Content-Type: application/json" \
     -d '{
  "document_type": "INVOICE",
  "invoice_id": "INV-2024-001",
  "invoice_date": "2024-10-24",
  "due_date": "2024-11-23",
  "currency": "EUR",
  "vendor_name": "Your Company BVBA",
  "vendor_tax_id": "BE0123456789",
  "vendor_address": "Main Street 123, 1000 Brussels, Belgium",
  "customer_name": "Customer Company NV",
  "customer_tax_id": "BE0987654321",
  "customer_address": "Customer Lane 456, 2000 Antwerp, Belgium",
  "items": [
    {
      "description": "Professional Services - Consulting services for October 2024",
      "quantity": "10",
      "unit_price": "100.00",
      "unit_code": "C62",
      "tax_rate": "21.00"
    }
  ]
}'

The example above will fail validation! This is intentional - it demonstrates why validation is critical. See below for the errors and how to fix them.

Response Types

Error Response (Real Example)

When validation fails, you’ll receive detailed UBL compliance errors. Here’s what the example above returns:

{
  "id": "b55354b0-5c69-489b-a8f7-44be7d5bdd6b",
  "file_name": "b55354b0-5c69-489b-a8f7-44be7d5bdd6b.xml",
  "is_valid": false,
  "issues": [
    {
      "message": "Belgian enterprise number MUST be stated in the correct format.",
      "type": "error",
      "rule_id": "PEPPOL-COMMON-R043",
      "flag": "fatal"
    },
    {
      "message": "[BR-S-08]-For each different value of VAT category rate (BT-119) where the VAT category code (BT-118) is \"Standard rated\", the VAT category taxable amount (BT-116) in a VAT breakdown (BG-23) shall equal the sum of Invoice line net amounts (BT-131)...",
      "type": "error",
      "rule_id": "BR-S-08",
      "flag": "fatal"
    },
    {
      "message": "Invoice line net amount MUST equal (Invoiced quantity * (Item net price/item price base quantity) + Sum of invoice line charge amount - sum of invoice line allowance amount",
      "type": "error",
      "rule_id": "PEPPOL-EN16931-R120",
      "flag": "fatal"
    }
  ]
}

This is exactly why the validation endpoint exists! These UBL BIS Billing 3.0 compliance errors would prevent your invoice from being sent. Let’s fix them.

Fixed Example

Here’s a corrected version that passes validation:

curl -X POST "https://api.e-invoice.be/api/validate/json" \
     -H "Authorization: Bearer YOUR_API_KEY" \
     -H "Content-Type: application/json" \
     -d '{
  "document_type": "INVOICE",
  "invoice_id": "INV-2024-001",
  "invoice_date": "2024-10-24",
  "due_date": "2024-11-23",
  "currency": "EUR",
  "vendor_name": "Your Company BVBA",
  "vendor_tax_id": "BE0897290877",
  "vendor_address": "Main Street 123, 1000 Brussels, Belgium",
  "customer_name": "Customer Company NV",
  "customer_tax_id": "BE0817331995",
  "customer_address": "Customer Lane 456, 2000 Antwerp, Belgium",
  "items": [
    {
      "description": "Professional Services - Consulting services for October 2024",
      "quantity": "10",
      "unit_price": "100.00",
      "unit_code": "C62",
      "tax_rate": "21.00",
      "amount": "1000.00"
    }
  ]
}'

What changed:

Valid Belgian VAT numbers with correct mod97 checksums:
- BE0897290877 (vendor) instead of BE0123456789
- BE0817331995 (customer) instead of BE0987654321
Added amount field to line items: "1000.00" (quantity × unit_price)

Success Response

When your JSON is valid, you’ll receive confirmation along with the generated UBL XML:

{
  "id": "9eec0b03-4649-4ae4-9c4c-323ebb6d53e8",
  "file_name": "9eec0b03-4649-4ae4-9c4c-323ebb6d53e8.xml",
  "is_valid": true,
  "issues": [],
  "ubl_document": "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n<Invoice xmlns=\"urn:oasis:names:specification:ubl:schema:xsd:Invoice-2\"..."
}

Response fields:

id: Validation session identifier
file_name: Generated XML filename
is_valid: true when validation passes
issues: Empty array when no errors
ubl_document: The generated UBL BIS Billing 3.0 XML (truncated above for readability)

Success means:

Your JSON is valid and UBL-compliant
You can see the exact UBL XML that will be generated
You’re ready to create the document using POST /api/documents/ with the same JSON payload

The ubl_document field shows you exactly what XML will be sent via Peppol. This is useful for debugging or understanding how your JSON maps to UBL BIS Billing 3.0.

Validating UBL XML

Use POST /api/validate/ubl to validate an existing UBL BIS Billing 3.0 XML file.

This endpoint expects multipart/form-data with a single file field — NOT a raw XML body. The most common integration mistake is sending the XML as the request body with Content-Type: application/xml, which returns a 422 with {"detail":[{"type":"missing","loc":["body","file"],"msg":"Field required"}]}. See common mistake below.

Request Contract


Method	`POST`
URL	`https://api.e-invoice.be/api/validate/ubl`
Authorization	`Bearer YOUR_API_KEY`
Content-Type	`multipart/form-data` (set automatically by your HTTP client when you attach a file)
Body	Form field `file` containing the UBL XML file (binary upload)

Copy-Paste Examples

curl -X POST "https://api.e-invoice.be/api/validate/ubl" \
     -H "Authorization: Bearer YOUR_API_KEY" \
     -F "file=@invoice.xml"

const fs = require('fs');
const FormData = require('form-data');
const axios = require('axios');

const form = new FormData();
form.append('file', fs.createReadStream('./invoice.xml'));

const response = await axios.post(
  'https://api.e-invoice.be/api/validate/ubl',
  form,
  {
    headers: {
      ...form.getHeaders(),
      Authorization: `Bearer ${process.env.E_INVOICE_API_KEY}`,
    },
  }
);

console.log(response.data);

import os
import requests

with open('invoice.xml', 'rb') as f:
    response = requests.post(
        'https://api.e-invoice.be/api/validate/ubl',
        headers={'Authorization': f"Bearer {os.environ['E_INVOICE_API_KEY']}"},
        files={'file': ('invoice.xml', f, 'application/xml')},
    )

print(response.json())

using System.Net.Http;
using System.Net.Http.Headers;

using var http = new HttpClient();
http.DefaultRequestHeaders.Authorization =
    new AuthenticationHeaderValue("Bearer", Environment.GetEnvironmentVariable("E_INVOICE_API_KEY"));

using var form = new MultipartFormDataContent();
var fileBytes = await File.ReadAllBytesAsync("invoice.xml");
var fileContent = new ByteArrayContent(fileBytes);
fileContent.Headers.ContentType = new MediaTypeHeaderValue("application/xml");
// IMPORTANT: the form field MUST be named "file"
form.Add(fileContent, "file", "invoice.xml");

var response = await http.PostAsync(
    "https://api.e-invoice.be/api/validate/ubl",
    form
);

Console.WriteLine(await response.Content.ReadAsStringAsync());

<?php
$ch = curl_init('https://api.e-invoice.be/api/validate/ubl');
curl_setopt_array($ch, [
    CURLOPT_RETURNTRANSFER => true,
    CURLOPT_POST => true,
    CURLOPT_HTTPHEADER => [
        'Authorization: Bearer ' . getenv('E_INVOICE_API_KEY'),
    ],
    CURLOPT_POSTFIELDS => [
        'file' => new CURLFile('invoice.xml', 'application/xml', 'invoice.xml'),
    ],
]);

echo curl_exec($ch);
curl_close($ch);

Response

Success (valid UBL):

{
  "id": "a1b2c3d4-5678-90ab-cdef-1234567890ab",
  "file_name": "invoice.xml",
  "is_valid": true,
  "issues": []
}

Validation errors:

{
  "id": "a1b2c3d4-5678-90ab-cdef-1234567890ab",
  "file_name": "invoice.xml",
  "is_valid": false,
  "issues": [
    {
      "message": "Invoice total amount mismatch",
      "type": "error",
      "rule_id": "BR-CO-15",
      "flag": "fatal",
      "schematron": "PEPPOL-EN16931"
    }
  ]
}

Common mistake: raw XML body

If you set Content-Type: application/xml and send the XML as the raw request body (e.g. --data-binary @invoice.xml), you’ll get this 422 response:

{
  "detail": [
    {
      "type": "missing",
      "loc": ["body", "file"],
      "msg": "Field required",
      "input": null
    }
  ]
}

The fix: switch to multipart/form-data with a file form field (as shown in the examples above).

Wrong	Right
`-H "Content-Type: application/xml" --data-binary @invoice.xml`	`-F "file=@invoice.xml"`
`requests.post(url, data=xml, headers={'Content-Type': 'application/xml'})`	`requests.post(url, files={'file': open('invoice.xml', 'rb')})`
`axios.post(url, xml, { headers: { 'Content-Type': 'application/xml' } })`	`axios.post(url, formData, { headers: formData.getHeaders() })`
`new StringContent(xml, ..., "application/xml")`	`new MultipartFormDataContent { { fileContent, "file", "invoice.xml" } }`

When to Use UBL Validation

Use POST /api/validate/ubl when you:

Have existing UBL XML files to verify before sending (e.g. generated by your ERP)
Are migrating from another Peppol Access Point with pre-generated UBL documents
Need to validate UBL files from external sources before posting them to /api/documents/ubl
Want to double-check the XML produced by /api/validate/json (the ubl_document field in that response)

If you’re creating invoices from JSON, prefer /api/validate/json — it validates the same UBL rules and returns the generated UBL alongside, so you don’t need a separate UBL validation call.

Common Validation Errors

Invalid Peppol ID Format

{
  "field": "vendor_tax_id",
  "message": "Invalid Peppol ID format. Expected: scheme:identifier"
}

Fix: Use the correct format scheme:identifier

Belgian companies: 0208:0123456789 (CBE number - VAT without ‘BE’ prefix)
See Peppol schemes

Invalid Tax Rate

{
  "field": "items[0].tax_rate",
  "message": "Invalid tax rate format. Must be a percentage string"
}

Fix: Use string format for tax rates:

Standard rate: "21.00"
Reduced rate: "6.00"
Zero rated: "0.00"

Missing Required Fields

{
  "field": "vendor_address",
  "message": "Field is required for UBL compliance"
}

Fix: Ensure all required fields are present:

Vendor/customer name, tax ID, and address
Invoice ID, invoice date, currency
At least one item with description, quantity, unit price, and tax rate

Invalid Date Format

{
  "field": "invoice_date",
  "message": "Invalid date format. Use ISO 8601: YYYY-MM-DD"
}

Fix: Use the format YYYY-MM-DD, e.g., 2024-10-24

Invalid Currency Code

{
  "field": "currency",
  "message": "Unsupported currency code"
}

Fix: Use supported ISO 4217 codes: EUR, USD, GBP, JPY, CHF, CAD, AUD, NZD, CNY, INR, SEK, NOK, DKK, SGD, HKD

Development Workflow

1. Build Your Invoice JSON

Start with a template or build your invoice object:

const invoice = {
  document_type: 'INVOICE',
  invoice_id: 'INV-2024-001',
  invoice_date: '2024-10-24',
  currency: 'EUR',
  // ... rest of invoice data
};

2. Validate First

Always validate before attempting to create:

const validation = await api.post('/api/validate/json', invoice);

if (!validation.data.is_valid) {
  console.error('Validation errors:', validation.data.issues);
  // Fix errors and try again
  return;
}

3. Create Document

Only after validation passes, create the document:

const document = await api.post('/api/documents/', invoice);

Complete Development Example

const axios = require('axios');

const api = axios.create({
  baseURL: 'https://api.e-invoice.be',
  headers: {
    'Authorization': `Bearer ${process.env.E_INVOICE_API_KEY}`,
    'Content-Type': 'application/json'
  }
});

async function validateAndCreateInvoice(invoiceData) {
  try {
    // Step 1: Validate the JSON
    console.log('Validating invoice JSON...');
    const validation = await api.post('/api/validate/json', invoiceData);

    if (!validation.data.is_valid) {
      console.error('❌ Validation failed:');
      validation.data.issues.forEach(issue => {
        console.error(`  - ${issue.rule_id}: ${issue.message}`);
      });
      return null;
    }

    console.log('✓ Invoice JSON is valid');

    // Step 2: Create the document
    console.log('Creating invoice...');
    const document = await api.post('/api/documents/', invoiceData);
    console.log('✓ Invoice created:', document.data.id);

    return document.data;

  } catch (error) {
    console.error('Error:', error.response?.data || error.message);
    return null;
  }
}

// Example usage - using valid data
const invoiceData = {
  document_type: 'INVOICE',
  invoice_id: 'INV-2024-001',
  invoice_date: '2024-10-24',
  due_date: '2024-11-23',
  currency: 'EUR',
  vendor_name: 'Your Company BVBA',
  vendor_tax_id: 'BE0897290877',  // Valid Belgian VAT with mod97 checksum
  vendor_address: 'Main Street 123, 1000 Brussels, Belgium',
  customer_name: 'Customer Company NV',
  customer_tax_id: 'BE0817331995',  // Valid Belgian VAT with mod97 checksum
  customer_address: 'Customer Lane 456, 2000 Antwerp, Belgium',
  items: [
    {
      description: 'Professional Services - Consulting services for October 2024',
      quantity: '10',
      unit_price: '100.00',
      unit_code: 'C62',
      tax_rate: '21.00',
      amount: '1000.00'  // Required: quantity × unit_price
    }
  ]
};

validateAndCreateInvoice(invoiceData);

Testing Strategy

During Development

Use /api/validate/json liberally:

Test edge cases: Validate unusual scenarios (zero amounts, multiple currencies, etc.)
Test all document types: Validate invoices, credit notes, and debit notes
Iterate quickly: Fix errors and re-validate without creating documents
Build test suites: Create automated validation tests

Before Production

Validate representative samples of all invoice types
Test with real customer Peppol IDs
Verify all tax categories and currency codes you’ll use
Test complex scenarios (allowances, charges, multiple line items)

Best Practices

Validate Early and Often

Don’t wait until production. Validate during development to catch issues early:

Test each new invoice template
Validate after schema changes
Include validation in CI/CD pipelines

Handle Validation Errors Gracefully

if (!validation.data.is_valid) {
  // Log detailed errors
  logger.error('Invoice validation failed', {
    invoice_id: invoiceData.invoice_id,
    issues: validation.data.issues
  });

  // Notify developers/users
  notifyError(validation.data.issues);

  // Don't attempt to create the document
  return;
}

Cache Validation Results

If you’re generating invoices from templates, validate the template once and cache the result:

const templateCache = new Map();

function validateTemplate(templateName, templateData) {
  if (templateCache.has(templateName)) {
    return templateCache.get(templateName);
  }

  const isValid = validateInvoiceJSON(templateData);
  templateCache.set(templateName, isValid);
  return isValid;
}

Use a Sandbox Company

Test validation extensively with a sandbox company before going live:

A sandbox company sends via email instead of Peppol, so testing is safe
Use the production API: https://api.e-invoice.be
Create a sandbox company from app.e-invoice.be

Next Steps

Create Invoices

Create and send validated invoices

Lookup Participants

Find valid Peppol IDs

Set Up Webhooks

Get notified about events

API Reference

Explore all endpoints

Getting started

Core guides

Alternative formats

Integration

Partners

Validation During Development

Overview

Why Validate?

Basic Validation

Response Types

Error Response (Real Example)

Fixed Example

Success Response

Validating UBL XML

Request Contract

Copy-Paste Examples

Response

Common mistake: raw XML body

When to Use UBL Validation

Common Validation Errors

Invalid Peppol ID Format

Invalid Tax Rate

Missing Required Fields

Invalid Date Format

Invalid Currency Code

Development Workflow

1. Build Your Invoice JSON

2. Validate First

3. Create Document

Complete Development Example

Testing Strategy

During Development

Before Production

Best Practices

Next Steps

Create Invoices

Lookup Participants

Set Up Webhooks

API Reference

​Overview

​Why Validate?

​Basic Validation

​Response Types

​Error Response (Real Example)

​Fixed Example

​Success Response

​Validating UBL XML

​Request Contract

​Copy-Paste Examples

​Response

​Common mistake: raw XML body

​When to Use UBL Validation

​Common Validation Errors

​Invalid Peppol ID Format

​Invalid Tax Rate

​Missing Required Fields

​Invalid Date Format

​Invalid Currency Code

​Development Workflow

​1. Build Your Invoice JSON

​2. Validate First

​3. Create Document

​Complete Development Example

​Testing Strategy

​During Development

​Before Production

​Best Practices

​Next Steps

Create Invoices

Lookup Participants

Set Up Webhooks

API Reference

Overview

Why Validate?

Basic Validation

Response Types

Error Response (Real Example)

Fixed Example

Success Response

Validating UBL XML

Request Contract

Copy-Paste Examples

Response

Common mistake: raw XML body

When to Use UBL Validation

Common Validation Errors

Invalid Peppol ID Format

Invalid Tax Rate

Missing Required Fields

Invalid Date Format

Invalid Currency Code

Development Workflow

1. Build Your Invoice JSON

2. Validate First

3. Create Document

Complete Development Example

Testing Strategy

During Development

Before Production

Best Practices

Next Steps