This recipe will redirect non-members from a specific "slug" to the levels page.

my-pmpro-redirect-non-members-to-another-page.php

<?php
/**
 * This recipe will redirect non-members from a specific page to the levels page.
 *
 * 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_pmpro_redirect_non_members_to_another_page() {

	if ( ! function_exists( 'pmpro_hasMembershipLevel' ) ) {
		return;
	}

	/**
	 * To set the page to redirect non-members from change members is_page( 'select-a-challenge' )
	 * to the relevant page slug, e.g.
	 * is_page( 'my-page-slug' ),
	 * or page ID, e.g.
	 * is_page( 124 )
	 */
	if ( is_singular( 'listing' ) && ! pmpro_hasMembershipLevel() ) {
		/**
		 * To redirect non-members to a different page than the PMPro levels page,
		 * replace pmpro_url( 'levels' ) 
		 * to target the relevant page slug, e.g.
		 * home_url( 'my-other-page-slug' ),
		 * @link https://developer.wordpress.org/reference/functions/home_url/
		 *
		 * or page ID, e.g.
		 * get_permalink( 82 )
		 * @link https://developer.wordpress.org/reference/functions/get_permalink/
		 */
		wp_redirect( pmpro_url( 'levels' ) );
		exit;
	}
}
add_action( 'template_redirect', 'my_pmpro_redirect_non_members_to_another_page' );