handler.php

См. документацию.

<?php
 
namespace Sale\Handlers\PaySystem;
 
use Bitrix\Main\Loader;
use Bitrix\Main\Localization\Loc;
use Bitrix\Sale;
use Bitrix\Sale\Payment;
use Bitrix\Sale\PaySystem;
use Bitrix\Crm\Integration;
 
PaySystem\Manager::includeHandler('orderdocument');
Loc::loadMessages(__FILE__);

class InvoiceDocumentHandler extends OrderDocumentHandler
{
    protected static function getDataProviderClass()
    {
        return Integration\DocumentGenerator\DataProvider\Invoice::class;
    }

    protected function getInvoiceNumber(Payment $payment)
    {
        $invoice = $payment->getOrder();
 
        return $invoice->getField('ACCOUNT_NUMBER');
    }
 
}