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 $wpdb, $pmpro_show_discount_code;

	if ( ! function_exists( 'pmpro_getLevelAtCheckout' ) || ! function_exists( 'pmpro_is_checkout' ) ) {
		return;
	}

	if ( pmpro_is_checkout() ) {
		$level = pmpro_getLevelAtCheckout();

		if ( ! empty( $level ) ) {

			$level_id = $level->id;

			$sql = $wpdb->prepare(
				"SELECT c.id
				FROM {$wpdb->pmpro_discount_codes} c
				LEFT JOIN {$wpdb->pmpro_discount_codes_levels} cl
				ON cl.level_id = c.id
				WHERE cl.level_id = %d",
				$level_id
			);

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

			if ( ! $results ) {
				$pmpro_show_discount_code = false;
			}
		}
	}
}
add_action( 'wp', 'mypmpro_show_discount_code_field_if_available' );