What is a billpayer on an order

[KodeStar]

I added an order, then when I went to the admin and to orders I got:
Call to a member function getName() on null
<?php echo e($order->billpayer->getName()); ?>
Despite there being no indication that billpayer was needed in the order docs https://vanilo.io/docs/3.x/orders, nor what the billpayer should look like.
So I figured I'd try using the factory instead as that is billed as handling all the necessary underlying details, but when I looked at the factory createBillpayer() is wrapped in if (isset($data['billpayer'])) { so unless billpayer is passed in the array it will never get created anyway.

I'm already creating a user as part of the checkout process (so they can log in), then creating a customer and tying it to that user, then creating an order and attaching the user_id to the order, now I need to create a billpayer and attach that to the order as well?

Looking at the tables there seems to be a fair bit of overlap in the columns between persons, customers and billpayers.

It's all a bit confusing at the moment.

[KodeStar]

Also all the references to Model are wrong, for example:

use Vanilo\Product\Model\Product;
use Vanilo\Order\Model\Order;

Should be

use Vanilo\Product\Models\Product;
use Vanilo\Order\Models\Order;