Ensure Paid Memberships Pro compatibility when using the Elementor Page Builder.

elementor_compatibility_for_pmpro.php

<?php
/**
 * Ensure Paid Memberships Pro compatibility when using the Elementor Page Builder: 
 * https://wordpress.org/plugins/elementor/
 *
 * Your administrator-level account must have a Membership Level in order to edit all of the pages assigned
 * under Memberships > Pages. 
 *
 * You must also set a Custom Field on the Membership Checkout page with the key 'pmpro_default_level' and 
 * value of a level ID in order to properly edit your Membership Checkout page using Elementor. 
 *
 * 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 elementor_compatibility_for_pmpro() {
 	if ( defined('PMPRO_VERSION') ) {
		// Remove the default the_content filter added to membership level descriptions and confirmation messages in PMPro.
		remove_filter( 'the_content', 'pmpro_level_description' );
		remove_filter( 'pmpro_level_description', 'pmpro_pmpro_level_description' );
		remove_filter( 'the_content', 'pmpro_confirmation_message' );
		remove_filter( 'pmpro_confirmation_message', 'pmpro_pmpro_confirmation_message' );

		// Filter members-only content later so that the builder's filters run before PMPro.
		remove_filter('the_content', 'pmpro_membership_content_filter', 5);
		add_filter('the_content', 'pmpro_membership_content_filter', 15);
	}
}
add_action( 'init', 'elementor_compatibility_for_pmpro' );

How do you set a custom field on the membership check out page?