This code can be used as a template for international businesses to create a custom VAT filter for WP Full Stripe. The example code takes into account the supplier’s and the buyer’s country to determine the VAT rate for e-goods.

vat-filter-example.php

<?php
/**
 * Determine the EU VAT rate based on country code
 *
 * @param string $country 2-letter ISO country code in uppercase
 * @return float  The VAT rate (percent) for the country
 */
 
function lookup_vat_rate_by_country($country) {
    switch ($country) {
        case 'LU':
            $vatPercent = 17.00;
            break;
 
        case 'MT':
            $vatPercent = 18.00;
            break;
 
        case 'CY':
        case 'DE':
            $vatPercent = 19.00;
            break;
 
        case 'GB':
        case 'AT':
        case 'EE':
        case 'FR':
        case 'RO':
        case 'SK':
        case 'SE':
            $vatPercent = 20.00;
            break;
 
        case 'BE':
        case 'BG':
        case 'CZ':
        case 'ES':
        case 'NL':
        case 'LT':
        case 'LV':
            $vatPercent = 21.00;
            break;
 
        case 'IT':
        case 'PT':
        case 'SI':
            $vatPercent = 22.00;
            break;
 
        case 'IE':
        case 'PL':
            $vatPercent = 23.00;
            break;
 
        case 'FI':
        case 'GR':
            $vatPercent = 24.00;
            break;
 
        case 'HR':
        case 'DK':
            $vatPercent = 25.00;
            break;
 
        case 'HU':
            $vatPercent = 27.00;
            break;
 
        default:
            $vatPercent = 0;
            break;
    }
 
    return $vatPercent;
}
 
/**
 * Determine the VAT rate based on default country, billing address, and custom fields
 *
 * @param float  $initialValue           Currently not used, always 0.
 * @param string $fromCountry            The default billing country, also the supplier's billing country
 * @param string $toCountry              The country of the billing address
 * @param array  $additionalArguments    A lot of additional info about the form, see below:
 *        The associative array has the following indexes:
 *                form_id
 *                form_type
 *                plan_id
 *                plan_currency
 *                plan_amount
 *                plan_setup_fee
 *                billing_address
 *                custom_inputs
 * @return float  The VAT rate, returned as a percent [0.0 .. 100.0]
 */
function determine_custom_vat_percent($initialValue, $fromCountry, $toCountry, $additionalArguments) {
    $euCountries = array('GB', 'LU', 'MT', 'CY', 'DE', 'RO', 'AT', 'EE', 'FR', 'SK', 'SE', 'BE', 'BG', 'CZ', 'ES', 'NL',
        'LT', 'LV', 'IT', 'PT', 'SI', 'IE', 'PL', 'FI', 'GR', 'HR', 'DK', 'HU');
 
 
    $customInputValues = array_key_exists('custom_inputs', $additionalArguments) ?
        $additionalArguments['custom_inputs'] : null;
 
    $b2bCustomer = isset($customInputValues) && is_array($customInputValues) &&
        (!empty($customInputValues['Company Name']) || !empty($customInputValues['VAT ID']));
 
 
    if (in_array($fromCountry, $euCountries)) {
        //-- Supplier is in the EU
        if (in_array($toCountry, $euCountries)) {
            // EU countries
            $domestic = $fromCountry === $toCountry;
 
            if ($b2bCustomer && !$domestic) {
                //-- B2B customer in EU
                $vatPercent = 0;
            } else {
                // B2C customer or domestic B2B in EU
                $vatPercent = lookup_vat_rate_by_country($toCountry);
            }
        } else {
            // Countries outside EU
            // B2B and B2C customers outside EU
            $vatPercent = 0;
        }
    } else {
        //-- Supplier is not in the EU
        if (in_array($toCountry, $euCountries)) {
            if ($b2bCustomer) {
                //-- B2B customer in EU
                $vatPercent = 0;
            } else {
                //-- B2C customer in EU
                $vatPercent = lookup_vat_rate_by_country($toCountry);
            }
        } else {
            //-- Outside EU, both B2B and B2C are 0%
            $vatPercent = 0;
        }
    }
 
    error_log("VAT percent: $vatPercent, from country: $fromCountry, to country: $toCountry");
 
    return $vatPercent;
}