NIP at Checkout

FCHub Fakturownia adds an optional "I want a company invoice" checkbox to the FluentCart checkout. When customers check it, a NIP (tax identification number) field appears. This is how Polish businesses provide their tax ID for a proper B2B VAT invoice.

How It Works

When the Checkout NIP Field setting is enabled (it is by default), the plugin adds two fields to the FluentCart checkout personal information section:

1. Checkbox -- "I want a company invoice" (billing_wants_company_invoice)
2. NIP input -- a text field for the Polish tax ID (billing_nip), hidden by default

Dynamic Rendering with MutationObserver

FluentCart renders its checkout form dynamically using JavaScript (Vue.js). This means the checkout fields don't exist in the DOM when the page first loads -- they're injected by FluentCart's JavaScript after initialization.

The plugin handles this by using a MutationObserver to watch for DOM changes:

var observer = new MutationObserver(function(mutations) {
    for (var i = 0; i < mutations.length; i++) {
        if (mutations[i].addedNodes.length) {
            initNipToggle();
            break;
        }
    }
});
observer.observe(document.body, { childList: true, subtree: true });

Every time FluentCart adds new nodes to the DOM (such as rendering or re-rendering the checkout form), the plugin re-initializes the NIP toggle behavior. This ensures the toggle/show functionality works regardless of when or how FluentCart renders the form.

The initNipToggle() function:

1. Finds the checkbox by its ID (billing_wants_company_invoice)
2. Finds the NIP wrapper using the [data-nip-field] attribute
3. Attaches a change event listener to show/hide the NIP field
4. Clears the NIP value when the toggle is unchecked

NIP Validation

The plugin validates NIP at checkout via the fluent_cart/checkout/validate_data filter. Invalid NIPs are rejected with a clear error message before the order is placed. The validation uses the official Polish mod-11 checksum algorithm.

The Algorithm

public static function validateNip(string $nip): bool
{
    $nip = preg_replace('/[^0-9]/', '', $nip);

    if (strlen($nip) !== 10) {
        return false;
    }

    $weights = [6, 5, 7, 2, 3, 4, 5, 6, 7];
    $sum = 0;

    for ($i = 0; $i < 9; $i++) {
        $sum += (int) $nip[$i] * $weights[$i];
    }

    $checkDigit = $sum % 11;

    // Mod-11 = 10 means no valid check digit exists
    if ($checkDigit === 10) {
        return false;
    }

    return $checkDigit === (int) $nip[9];
}

Data Storage

The NIP and company invoice preference are stored in the billing address metadata within FluentCart's order system.

Storage Location

The data is stored in the fct_order_addresses table, specifically in the meta JSON column under other_data:

{
  "other_data": {
    "wants_company_invoice": true,
    "nip": "1234563218"
  }
}

How the Invoice Handler Reads It

When creating an invoice, the InvoiceHandler reads the NIP from the billing address:

$nip = $billingAddress
    ? Arr::get($billingAddress->meta ?? [], 'other_data.nip', '')
    : '';

If nip is non-empty, a B2B invoice is created. Otherwise, it's a B2C invoice.

The checkbox state (wants_company_invoice) is not used for B2B detection — it's injected via raw DOM outside Vue's reactive system and its state is never persisted to POST data. The NIP value alone determines the invoice type. The checkbox exists purely as a UX toggle to show/hide the NIP field.

Checkout Field Schema

The plugin registers two fields through FluentCart's checkout field schema system.

The NIP field is also registered in FluentCart's address field system (fluent_cart/fields/address_base_fields) so it appears correctly in saved address displays. This registration is limited to billing addresses only.

GDPR Considerations

Key points for GDPR compliance:

• Purpose -- NIP is collected specifically for invoice generation as required by Polish tax law. This is a legitimate interest / legal obligation basis.
• Storage -- NIP is stored in FluentCart's order address metadata. It persists as long as the order record exists.
• Deletion -- when you delete an order in FluentCart, the associated address metadata (including NIP) is deleted. Uninstalling the plugin also removes Fakturownia-related order metadata.
• Disclosure -- inform customers in your privacy policy that their NIP may be shared with Fakturownia for invoice generation and (if applicable) submitted to KSeF.

Disabling the NIP Field

If you don't need the NIP checkout field (for example, if you only sell to consumers or handle NIP collection through other means), you can disable it:

1. Go to FluentCart > Settings > Integrations > Fakturownia
2. Set Checkout NIP Field to No
3. Save settings

When disabled, the CheckoutFields::register() method returns early without registering any hooks. No checkbox or NIP field will appear at checkout, and all invoices will be created as B2C.