Gravity Perks // GP Unique ID // Add Wait-for-payment Support for 3rd-party Payment Gateways

gp-unique-id-wait-for-payment-3rd-party.php

<?php
/**
 * Gravity Perks // GP Unique ID // Add Wait-for-payment Support for 3rd-party Payment Gateways
 * http://gravitywiz.com/documentation/gp-unique-id/
 */

// 1 - Indicate that waiting for payments is enabled.
add_filter( 'gpui_wait_for_payment', '__return_true' );

// 2 - Fetch the applicable payment feed for your gateway.
add_filter( 'gpui_wait_for_payment_feed', function( $feed, $form, $entry ) {
	// Replace the get_my_payment_feed_func() with your own functionality for fetching your payment feed.
	$feed = get_my_payment_feed_func();
	return $feed;
}, 10, 3 );

// 3 - Call populate_field_value() with the $fulfilled flag set to true when the payment is completed.
// This example is how it works with the Gravity Forms PayPal add-on. When the payment is fulfilled, 
// PayPal triggers the gform_paypal_fulfillment action. We bind to that action and call the 
// populate_field_value() method to populate the unique ID when the payment is fulfilled.
add_action( 'gform_paypal_fulfillment', function( $entry ) {
	$form = GFAPI::get_form( $entry['form_id'] );
	gp_unique_id_field()->populate_field_value( $entry, $form, true );
}, 9 );

Does this code actually work, or is this rather a draft? How should I redirect to a third party payment gateway and - in return - from a configured callback script back to the form in Wordpress?

Do I create this PHP file within the GP Unique ID folder on my server? Basically I'm needing to know where does this code go? I put it into my functions.php so I'll see how it goes. However, if it's in the wrong place, again, let me know.