<?php
  /** This function works with WooCommerce URL Coupons
    * When a coupon gets deferred, it's added to a list of deferred_url_coupons.
    * This function accepts a coupon ID ($coupon_id) as an argument, and gets all of the deferred_coupons
    * as an array. The coupon ID would be an array key,which is what this function checks for.
    * A message is printed. nothing is returned.
  **/
  function get_deferred_coupons( $coupon_id ) {
    global $woocommerce;

    $deferred_coupons = $woocommerce->session->get( 'deferred_url_coupons', array() );

    if( array_key_exists( $coupon_id,  $deferred_coupons ) ) {
      echo '<p>Hey! Your coupon will be automattically applied at checkout!</p>';
    }
  }