Get on sale product IDs for Repeater

get_on_sale_wc_products_ids.php

<?php
/**
 * Getting on sale product ids
 * @use wc_get_product_ids_on_sale function
 * return string
 */
function ouwoo_wc_get_product_ids_on_sale() {
    return implode( ",", (array) wc_get_product_ids_on_sale() );
}