Who referred you to our site? field for PMPro Register Helper

pmpro-register-helper-fields.php

<?php
/*
Plugin Name: Paid Memberships Pro - Custom Register Helper Fields
Plugin URI: https://www.paidmembershipspro.com/documentation/register-helper-documentation/code-examples/
Description: Register Helper Fields
Version: .1
Author: Stranger Studios
Author URI: http://www.strangerstudios.com
*/
//we have to put everything in a function called on init, so we are sure Register Helper is loaded
function my_pmprorh_init()
{
	//don't break if Register Helper is not loaded
	if(!function_exists( 'pmprorh_add_registration_field' )) {
		return false;
	}
	
	//define the fields
	$fields[] = new PMProRH_Field(
		'referral',         // input name, will also be used as meta key
		'text',				// type of field
		array(
			'label'		=> 'Who referred you to our site?',	 // custom field label
			'profile'	=> 'admin',					// only show in profile for admins
			'memberslistcsv' => true,						//include in csv exports
		)
	);
	
	//add the fields into a new checkout_boxes are of the checkout page
	foreach($fields as $field)
		pmprorh_add_registration_field(
			'checkout_boxes',				// location on checkout page
			$field							// PMProRH_Field object
		);
	
	//that's it. see the PMPro Register Helper readme for more information and examples.
}
add_action( 'init', 'my_pmprorh_init' );

This recipe is included in the blog post on "How to add a custom referral field to your membership site and how it can help you grow your business." at Paid Memberships Pro here: https://www.paidmembershipspro.com/how-to-add-a-custom-referral-field-to-your-membership-site-and-how-it-can-help-you-grow-your-business/