mypmpro-hide-discount-field-not-available.php

<?php
/**
 * This recipe will hide the discount code field on the checkout page if no discount codes 
 * have been created for that specific level.
 * 
 * You can add this recipe to your site by creating a custom plugin
 * or using the Code Snippets plugin available for free in the WordPress repository.
 * Read this companion article for step-by-step directions on either method.
 * https://www.paidmembershipspro.com/create-a-plugin-for-pmpro-customizations/
 */

function mypmpro_show_discount_code_field_if_available(){
	
	global $pmpro_pages, $wpdb, $pmpro_show_discount_code;

	if( is_page( intval( $pmpro_pages['checkout'] ) ) ) {

		if( !empty( $_REQUEST['level'] ) ){

			$level_id = intval( $_REQUEST['level'] );

			$sql = "SELECT * FROM $wpdb->pmpro_discount_codes_levels cl 
					LEFT JOIN $wpdb->pmpro_discount_codes c
					ON cl.level_id = c.id WHERE cl.level_id = '$level_id'";

			$results = $wpdb->get_results( $sql );

			if( !$results ) {				
				$pmpro_show_discount_code = false;	
			}

		}

	}

}
add_action( 'wp', 'mypmpro_show_discount_code_field_if_available' );