I am making a WordPress plugin that works with WooCommerce. I have a database table with discount codes. With this code my customer can buy 10 tickets for a movie. This could mean he orders 10 tickets in a single order, or five orders with two tickets each. I am trying to get the POST data from WooCommerce when I fill in a discount code, but I can't get it to work. function strippenkaart_apply_discount($cart) { error_log('POST-gegevens: ' . json_encode($_POST)); // checks if coupon code is found - then apply discount } add_action('woocommerce_cart_calculate_fees', 'strippenkaart_apply_discount'); I do not receive any POST data. What am I doing wrong? Logs: POST-gegevens: []