Add Facebook Email Field on Checkout

facebook_email_on_checkout.php

<?php

//Add from here down to the bottom of your PMProcustomizations plugin

function my_pmprorh_init() {
	// don't break if Register Helper is not loaded.
	if ( ! function_exists( 'pmprorh_add_registration_field' ) ) {
		return false;
	}

	// define the field.
	$facebook_email = new PMProRH_Field(
		'facebook_email',              // input name, will also be used as meta key.
		'text',                        // type of field.
		array(
			'label'    => 'Which email address do you use for your Facebook Account',  // custom field label.
			'size'     => 40,            // input size.
			'profile'  => true,          // show in user profile.
			'required' => false,         // make this field required.
		)
	);

	pmprorh_add_registration_field(
		'after_email',  // location on checkout page.
		$facebook_email    // PMProRH_Field object.
	);
}
add_action( 'init', 'my_pmprorh_init' );