WooCommerce Currency Switcher - Set currency for legacy API

/**
 * Aelia Currency Switcher - Force currency for legacy API calls.
 *
 * HOW TO USE THIS CODE
 * Simply add the code to the bottom of your theme's functions.php file, and it
 * will run automatically. For more information: https://www.skyverge.com/blog/add-custom-code-to-wordpress/
 *
 * GPL DISCLAIMER
 * Because this code program is free of charge, 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.
 *
 * Need a consultation, or assistance to customise this code? Find us on Codeable: https://aelia.co/hire_us
 */

/**
 * Forces the selected currency to GBP for legacy API requests, unless another
 * currency was passed via the URL.
 *
 * @param string selected_currency
 * @return string
 */
function aelia_set_currency_for_api_calls($selected_currency) {
  // Force selected currency to GBP for API calls, unless a
  // currency was passed via the URL
  if(empty($_GET['aelia_cs_currency'])) {
    $selected_currency = 'GBP';
  }
  return $selected_currency;
}

/**
 * Intercepts legacy API requests to force the currency to GBP, bypassing geolocation.
 *
 * @param string api_request
 */
add_action('woocommerce_api_request', function($api_request) {
  add_filter('wc_aelia_cs_selected_currency', 'aelia_set_currency_for_api_calls', 30);
}, 10, 1);