Donate to specific categories or causes using PMPro User Fields

my_pmpro_checkout_donations.php

<?php
/**
 * Donate to specific categories or causes using PMPro User Fields. This is different and independent from the PMPro Donations 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/
 */

function my_pmpro_checkout_donations($level)
{
    $donation = 0;
    
    if (!empty($_REQUEST['donation_to_emma']) && is_numeric($_REQUEST['donation_to_emma'])) {
        $donation = $donation + $_REQUEST['donation_to_emma'];
    }
    
    if (!empty($_REQUEST['donation_to_piper']) && is_numeric($_REQUEST['donation_to_piper'])) {
        $donation = $donation + $_REQUEST['donation_to_piper'];
    }
    
    $level->initial_payment = $level->initial_payment + $donation;
    
    return $level;
}
add_filter("pmpro_checkout_level", "my_pmpro_checkout_donations");

function my_pmpro_checkout_donation_fields()
{
    // Don't break if PMPro is out of date or not loaded.
    if (!function_exists('pmpro_add_user_field')) {
        return false;
    }
    
    // membership level IDs to show donation fields on
    $show_donation_levels = array(1,2,3);
    
    //define the fields
    $fields   = array();
    $fields[] = new PMPro_Field('donation_to_emma', 'text', array(
        'label' => 'Donation to Emma',
        'size' => 7,
        'profile' => 'admin_only',
        'levels' => $show_donation_levels
    ));
    
    $fields[] = new PMPro_Field('donation_to_piper', 'text', array(
        'label' => 'Donation to Piper',
        'size' => 7,
        'profile' => 'admin_only',
        'levels' => $show_donation_levels
    ));
    
    pmpro_add_field_group("donations", "Donations");
    
    //add the fields into the donations field group
    foreach ($fields as $field) {
        pmpro_add_user_field('donations', $field);
    }
    
}
add_action('init', 'my_pmpro_checkout_donation_fields');