Add the PMPro meta box to a CPT. Add this to your plugin/etc.

pmpro-cpt.php

<?php
/**
 * Add the PMPro meta box to a CPT
 *
 * 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 my_add_pmpro_meta_box_to_cpts() {
	// Duplicate this row for each CPT. This one adds the meta boxes to 'advert' CPTs.
	add_meta_box('pmpro_page_meta', 'Require Membership', 'pmpro_page_meta', 'advert', 'side' );
}
add_action( 'admin_menu', 'my_add_pmpro_meta_box_to_cpts', 20 );