EU VAT Assistant - Validate EU VAT number via code

/**
 * Aelia EU VAT Assistant for WooCommerce - Validate VAT numbers via code.
 * This code shows how to use the EU VAT Assistant to call the VIES service to validate a EU VAT number.
 * DISCLAIMER
 * This code is free of charge and there is no warranty for it, to the extent permitted by applicable law.
 * Except when otherwise stated in writing the copyright holders and/or other parties provide the program "as is"
 * without warranty of any kind, either expressed or implied, including, but not limited to, the implied warranties of
 * merchantability and fitness for a particular purpose. The entire risk as to the quality and performance of the program
 * is with you. should the program prove defective, you assume the cost of all necessary servicing, repair or correction.
 *
 * The code is provided as an example and it's not covered by our support service. We won't be able to offer free support
 * in relation to it. Should you need a consultation, or assistance to customise this code, you can contact us to avail
 * of our paid consultation services: https://aelia.co/contact
 */

// Basic validation of a VAT number
$vat_number_valid = apply_filters('wc_aelia_eu_vat_assistant_validate_vat_number', $vat_number_valid, $country, $vat_number);

// Possible responses
const VAT_NUMBER_VALIDATION_NO_NUMBER = 'no-number';
const VAT_NUMBER_VALIDATION_VALID = 'valid';
const VAT_NUMBER_VALIDATION_NOT_VALID = 'not-valid';
const VAT_NUMBER_VALIDATION_NON_EU = 'non-eu';
const VAT_NUMBER_COULD_NOT_BE_VALIDATED = 'could-not-be-validated';
const VAT_NUMBER_ENTERED_MANUALLY_NOT_VALIDATED = 'entered-manually-not-validated';

// Validation of a VAT number, returning the raw response. The response will
// be an array with the data returned by the VIES service. You will have to parse
// such response yourself to extract the necessary data
$response = apply_filters('wc_aelia_eu_vat_assistant_validate_vat_number', $vat_number_valid, $country, $vat_number, true);

// Validation of a VAT number, returning the raw response, passing the requester VAT number. This will
// return the consultation number as part of the response, in $response['raw_response']['requestidentifier']
$response = apply_filters('wc_aelia_eu_vat_assistant_validate_vat_number', $vat_number_valid, $country, $vat_number, true, $requester_country, $requester_vat_number);


// Sample response
/*
array (size=6)
  'valid' => boolean true
  'company_name' => string ''
  'company_address' => string ''
  'errors' =>
    array
      0 => string ''
  'raw_response' =>
    array
      'countrycode' => string 'GB'
      'vatnumber' => string '12345678901234'
      'requestdate' => string '2020-01-01+00:00'
      'valid' => string 'true'
      'tradername' => string 'John, Doe'
      'tradercompanytype' => string '---'
      'traderaddress' => string '1 Main Street, London'
      'requestidentifier' => string 'WAPIAAABBBCCCDDDEEE'
      'euva_validation_result' => string 'valid'
*/