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VAT Number Verification for B2B Vendor and Supplier Onboarding

Validating supplier VAT numbers during vendor onboarding prevents incorrect tax treatment on purchase invoices, flags shell suppliers, and satisfies EU record-keeping requirements. Use the TaxID API to automate VAT checks in your vendor management workflow.

Implementation steps

1. 1

   Add VAT validation to the vendor registration form

   When a new vendor submits their details via your supplier portal or ERP onboarding form, trigger a TaxID API call immediately on VAT number submission. Display the validated company name and address to the vendor for confirmation — this catches transposition errors and confirms they have provided the correct number for the legal entity invoicing you.

2. 2

   Gate vendor activation on validation status

   Only activate vendors with status: 'active'. For vendors returning service_unavailable (VIES temporarily down), hold the vendor record as 'pending validation' and auto-retry within 24 hours. For vendors returning invalid or inactive, route the record to manual review with the validation failure reason — do not silently activate.

3. 3

   Store the validation record in the vendor master

   Persist vat_number, company_name, address, validation_status, request_id, and validated_at in the vendor master data record. For ERP systems, map these fields to the appropriate vendor master data fields (or custom fields if the ERP does not natively support them). This provides an auditable record of due diligence at the point of onboarding.

4. 4

   Run monthly batch re-validation of all active vendors

   Schedule a monthly batch job using the TaxID batch endpoint to re-validate all VAT numbers in your vendor master. Flag vendors whose status has changed from active to inactive or invalid for procurement review before their next invoice is processed. This is particularly important for markets like Romania and Bulgaria where supplier VAT deregistrations are more frequent.

5. 5

   Integrate with invoice matching workflow

   For three-way matching systems (PO → receipt → invoice), add a VAT validation check as part of invoice approval. If an invoice arrives from a vendor whose VAT number has become invalid since onboarding, flag the invoice for AP review before payment. The input VAT deduction on that invoice may need to be reversed.

Code example

const res = await fetch(
  'http://localhost:3000/api/v1/validate/DE/DE123456789',
  { headers: { 'Authorization': 'Bearer YOUR_API_KEY' } }
);
const { valid, status, company_name, company_address } = await res.json();

if (valid) {
  console.log(`Valid EU business: ${company_name}`);
} else if (status === 'service_unavailable') {
  // VIES is temporarily down — retry or allow with manual check
  console.log('VIES unavailable — check back in a few minutes');
} else {
  console.log('Invalid VAT number — charge local tax rate');
}

import requests

res = requests.get(
    "http://localhost:3000/api/v1/validate/DE/DE123456789",
    headers={"Authorization": "Bearer YOUR_API_KEY"}
)
data = res.json()

if data["valid"]:
    print(f"Valid: {data['company_name']}")
elif data["status"] == "service_unavailable":
    print("VIES temporarily unavailable")
else:
    print("Invalid VAT number")

API response

The TaxID API returns a consistent JSON response for every validation request:

{
  "valid": true,
  "status": "active",
  "country_code": "DE",
  "vat_number": "123456789",
  "company_name": "Example GmbH",
  "company_address": "Musterstraße 1, 10115 Berlin",
  "request_date": "2026-05-10T00:00:00.000Z",
  "cached": false,
  "request_id": "req_01j..."
}

Error handling

The API uses a consistent Stripe-style error format. Always handle service_unavailable separately — VIES has occasional downtime and you should not reject valid customers during outages.

Evaluating EU VAT APIs? Compare TaxID vs Vatstack, Vatlayer, Avalara →

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