Custom order data example - Order attributes filter

wps-custom-order-data-attrs.php

<?php

/*

Step 3. Saves any dynamic session variables to the Shopify order. Fires once the user clicks the checkout button.

*/
function namespace_cart_checkout_attrs() {

  // Gain access to the global $_SESSION variable
  if (session_status() == PHP_SESSION_NONE) {
    session_start();
  }

  // Check to make sure our unique Session variable exists first
  if ( isset($_SESSION['dynamic_values']) && $_SESSION['dynamic_values'] ) {
    return $_SESSION['dynamic_values'];
  }

}

add_filter('wps_cart_checkout_attrs', 'namespace_cart_checkout_attrs');