functions.php

functions.php

/**
 * Schedule the daily event if necessary.
 */
function schedule_delete_expired_coupons() {
	if ( ! wp_next_scheduled( 'delete_expired_coupons' ) ) {
		wp_schedule_event( time(), 'daily', 'delete_expired_coupons' );
	}
}
add_action( 'init', 'schedule_delete_expired_coupons' );

/**
 * Trash all expired coupons when the event is triggered.
 */
function delete_expired_coupons() {
	$args = array(
		'posts_per_page' => -1,
		'post_type'      => 'shop_coupon',
		'post_status'    => 'publish',
		'meta_query'     => array(
			'relation'   => 'AND',
			array(
				'key'     => 'date_expires',
				'value'   => current_time( 'timestamp' ),
				'compare' => '<='
			),
			array(
				'key'     => 'date_expires',
				'value'   => '',
				'compare' => '!='
			)
		)
	);

	$coupons = get_posts( $args );

	if ( ! empty( $coupons ) ) {
		foreach ( $coupons as $coupon ) {
			wp_trash_post( $coupon->ID );
		}
	}
}
add_action( 'delete_expired_coupons', 'delete_expired_coupons' );

Change "expiry_date" to "date_expires"