How to Validate VAT Numbers in Real Time in Gravity Forms

1. What You’ll Need
2. 1 — Create a Connection Profile
   1. Create the Endpoint
3. 2 — Build VAT Validation Form
   1. Add Form Fields
   2. Connect GP Populate Anything to GC API Alchemist
   3. Add Feedback Messages
   4. Show/Hide Submit Button
4. 3 — Prevent Tampering
5. 4 — Test Drive
6. Wrapping Up

VAT Numbers keep you compliant and your invoices accurate. But let’s be real, manually validating them is tedious. One invalid VAT number can mean compliance issues and extra admin work you don’t need.

But, what if you could validate VAT numbers instantly, catching errors before they happen?

Today, we’re going to brew a solution using GC API Alchemist, which bridges Gravity Forms with any API—including VAT validation services. We’ll pair it with GP Populate Anything which handles the real-time validation. It sends the VAT number to the API, gets the result, and updates the form instantly. 

Together? They create a vigilant VAT validator. 🦸

What You’ll Need

1. GC API Alchemist: connects the form to a VAT validation API.
2. GP Populate Anything: pings the API after the users type and stores the result.
3. Conditional Logic: shows/hides the submit button based on validity.
4. A magical snippet: prevents tampering with the validation result.
5. A free account at EU VAT API.

1 — Create a Connection Profile

First, we’ll connect GC API Alchemist to the VAT validation API. We’re using the EU VAT API for this guide.

1. Open your Spellbook › activate GC API Alchemist.
2. Navigate to Forms › API Connections.
3. Click Add New API Connection to create the profile.
4. In General:
   • Base URL: https://euvatapi.com/api/v1/
   • Description: EU VAT Number Validation

5. In Authentication:
   • Type: API Key
   • Head to https://euvatapi.com/ › copy your API key › paste.
   • Key Location: Query Parameter
   • Key Name: access_key

6. Click Publish.

Create the Endpoint

But what is an endpoint? Think of it as a specific question you’re asking the API. You send info (VAT number) and specify what answer you want back (whether it’s valid).

7. In the new connection profile › click Create Endpoint.
8. In Configuration:
   • Name: VAT Validator
   • API Endpoint: validate — this creates https://euvatapi.com/api/v1/validate
   • Click Next.

9. In Data & Property Mapping › skip for now › click Next.
10. In Query Parameters & Filters:
    • Click Add Parameter.
    • Parameter Name: vat_number — this is data the API will use to validate against.
    • Click Next.

11. Data & Property Mapping (Round 2):
    • You’ll see the new vat_number parameter.
    • Enter a test number: FR40303265045
    • The API auto-tests and shows the full response data.
    • Leave property mapping as-is › click Next.

12. Query Parameters & Filters (Round 2) › click Next.
13. In Cache Settings: Leave caching enabled — saves API calls and tokens.
14. Click Create Endpoint.

Alright! You’ve now taught GC API Alchemist the language it needs to speak with the VAT API.

2 — Build VAT Validation Form

Let’s create the form where users enter the VAT numbers and where GP Populate Anything validates them in real-time.

Add Form Fields

1. Open your Spellbook › activate GP Populate Anything.
2. Create a new form (or edit an existing one).
3. Add a Single Line Text field:
   • Label: VAT Number
4. Add another Single Line Text field (this will store the result):
   • Label: Is VAT Valid?
   • Go to Advanced › Visibility › set to hidden.
   • Check Allow field to be populated dynamically.

Connect GP Populate Anything to GC API Alchemist

5. Still in the Is VAT Valid? field › enable Populate value dynamically.
6. Configure Population:
   • Type: API Alchemist
   • Connection Profile: EU VAT API
   • Endpoint: VAT Validator
   • Add Filter Group › set to vat_number is VAT Number field.
   • Value Templates: Set to valid (this pulls the validation result from the API)

Add Feedback Messages

We can control the feedback messages using conditional logic.

7. Add an HTML field:
   • Content: VAT number is valid ✅
   • Enable Conditional Logic: Show if All match: Is VAT valid? is 1 (1 means true)

8. Add another HTML field:
   • Content: VAT number is invalid ❌
   • Enable Conditional Logic: Show if All match: Is VAT valid is not 1
   • Add another condition: VAT Number is not [leave empty] — this prevents showing the error when field is blank.

Show/Hide Submit Button

Let’s hide that submit button until the VAT number checks out.

9. Click the Submit button to edit.
10. Enable Conditional Logic
11. Show if All match: Is VAT valid? is 1

3 — Prevent Tampering

A tech-savvy user could open the browser’s tools and manually change the value in the hidden field. To prevent this, we’ll use the force repopulation snippet that’ll force the form to double-check with the API one last time right before the form is submitted.

1. Go to Plugins › Add New › search for Code Snippets › install and activate.
2. Navigate to Snippets › Add New.
3. Copy the force repopulation snippet code.
4. Paste the code into the new snippet.
5. Add a title › Force Repopulation
6. Save and Activate.

Now, when someone submits the form, the VAT number will be checked one more time on the server. If someone tries to cheat by changing the hidden field, the system will catch it and check again. 👮

4 — Test Drive

Let’s make sure everything works.

1. Preview the form.
2. Enter an invalid VAT number — try GB999999999
   • Invalid message appears
   • Submit button stays hidden
3. Enter a valid VAT number — try FR40303265045
   • Valid message appears
   • Submit button shows up

If all works as expected, you’re done!

Wrapping Up

Let’s do a quick recap of what we just built.

• Connected Gravity Forms to a live VAT validation API.
• Validated user input VAT numbers in real-time thanks to GP Populate Anything.
• Secured the form against invalid submissions.

And VAT’s a wrap! Give yourself a pat on the back. 🙌