Require a sponsor code for the "child" level checkout when using Paid Memberships Pro and the Sponsored/Group Membership Add On.

pmprosm_discount_code_required.php

<?php
/*
 * Require a sponsor code for the "child" level checkout when using 
 * Paid Memberships Pro and the Sponsored/Group Membership Add On.
 *
 * 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/
 *
 */
global $pmprosm_sponsored_account_levels;
$pmprosm_sponsored_account_levels = array(
	1 => array(
		'main_level_id' => 1,
		'sponsored_level_id' => 2,
		'seats' => 10,
		'discount_code_required' => true,

	),
);

This recipe is included in the blog post on "Require a Sponsor Code for Checkout for a Sponsored Membership Level" at Paid Memberships Pro here: https://www.paidmembershipspro.com/require-a-sponsor-code-for-checkout-for-a-sponsored-membership-level/