Add Initial Payment column to PMPro v3 Members List Export CSV

my_pmpro_members_list_initial_payment_column.php

<?php
/**
 * Add Initial Payment to Members List Export CSV
 *
 * 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/
 * 
 */
// add the initial_payment column to the export
function my_pmpro_members_list_csv_extra_columns( $columns ) {

	$columns["initial_payment"] = "my_pmpro_members_list_initial_payment_column";
	return $columns;

}
add_filter( 'pmpro_members_list_csv_extra_columns', 'my_pmpro_members_list_csv_extra_columns', 10 );

// call back to get the initial payment amount
function my_pmpro_members_list_initial_payment_column( $user ) {

	$subscriptions = PMPro_Subscription::get_subscriptions_for_user( $user->ID, $user->membership_id );
	$initial_payment = empty( $subscriptions  ) ? '' : $subscriptions[0]->get_initial_payment();
	return $initial_payment;

}