---
title: UK VAT Validation Fails
description: UK VAT numbers failing with Validation failed in WooCommerce? The cause is usually the UK validation service. How to fix it.
url: "https://wpfactory.com/docs/uk-vat-validation-fails/"
updated: "2026-09-26"
category: Troubleshooting
tags:
  - EU VAT Manager for WooCommerce
---

# UK VAT Validation Fails

If UK VAT numbers fail validation in [EU/UK VAT Manager for WooCommerce](https://wpfactory.com/item/eu-vat-for-woocommerce/), add a VATSense API key at **WPFactory > EU VAT** (also reachable at **WooCommerce > Settings > EU VAT**) > **Validation** > **VATSense.com API key**. UK numbers skip VIES: every `GB` number goes to VATSense, and without a key the check cannot run.

## Symptoms

- "VAT is not valid." (or, on older versions, "Validation failed. Please try again.") for a UK number you know is valid.
- Previously valid UK VAT numbers are rejected.
- The problem affects many UK numbers, not one specific customer, while EU numbers still validate.

## Cause

UK VAT numbers are not validated through VIES. The plugin validates them through VATSense. If no VATSense API key is configured, or the key is invalid or out of credit, UK validation gets no answer and the number is treated as not valid, while EU validation keeps running.

## Fix

1. **Update the plugin** to the latest version, so it uses the current UK validation path.
2. **Add a VATSense API key.** Get a key at [vatsense.com](https://vatsense.com/) and enter it in **VATSense.com API key** on the **Validation** sub-tab at **WPFactory > EU VAT** (also reachable at **WooCommerce > Settings > EU VAT**). The same key covers the UK, Australia, Norway and Switzerland.
3. **Check the number format.** Use the `GB` prefix followed by the digits, with no spaces, or enable **Allow VAT number input with non-alphanumeric symbols**.
4. **Check the billing country.** If **Check for matching billing country code** is on, the billing country must be United Kingdom (UK) for a `GB` number.
5. **Clear caches** (server, CDN, caching plugin) and test a UK number you know is valid, in a new private window so a cached session result is not reused.
6. If it still fails, turn on **Debug** on the Advanced sub-tab, reproduce the check, and look in **WooCommerce > Status > Logs**. An entry such as "Error: VAT ID not valid" means VATSense answered; "Something went wrong" points to the key or the connection.

## UK and non-EU options

| Option (Validation sub-tab) | Default | Used for |
| --- | --- | --- |
| VATSense.com API key | Empty | GB, AU, NO and CHE numbers (always) and the EU fallback |
| Enable VATSense fallback | Off | EU numbers only, when VIES gives no answer |
| Allow VAT number input without country code | Off | Needed for Australian numbers |

**Enable VATSense fallback** does not affect UK numbers: they always go to VATSense. Turn it on only if you also want VATSense to answer when VIES is down.

## FAQ

### Do I need a paid VATSense plan?

That depends on your volume and VATSense's own plans. The plugin only needs a working API key.

### What about Northern Ireland (XI) numbers?

Only GB, AU, NO and CHE prefixes are routed to VATSense. Other prefixes, including XI, go through VIES.

### Is UK validation a Pro feature?

No. The VATSense options are in the free version.

Related: [Validate UK and Non-EU VAT Numbers with VATSense](https://wpfactory.com/docs/vatsense-non-eu-validation/) and [EU VAT Validation Always Fails](https://wpfactory.com/docs/eu-vat-validation-fails/).

Need a hand? Our team answers every ticket on the [EU/UK VAT Manager support forum](https://wpfactory.com/support/item/eu-vat-for-woocommerce/).

Related articles

- [VIES VAT Validation Blocked (IP_BLOCKED): Alternative VAT Validation in WooCommerce](https://wpfactory.com/docs/vies-ip-blocking/)
- [Customize the VAT Validation Messages](https://wpfactory.com/docs/customize-vat-validation-messages/)
- [EU VAT Validation Options in WooCommerce](https://wpfactory.com/docs/streamline-eu-vat/)
- [Configuring EU VAT Validation](https://wpfactory.com/docs/configure-eu-vat-validation/)
- [VAT Not Removed After Entering a Valid VAT Number](https://wpfactory.com/docs/eu-vat-not-removed-valid-number/)

 

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