invoiceninja/app/Ninja/Import/CSV/PaymentTransformer.php

<?php namespace App\Ninja\Import\CSV;

use App\Ninja\Import\BaseTransformer;
use League\Fractal\Resource\Item;

class PaymentTransformer extends BaseTransformer
{
    public function transform($data)
    {
        return new Item($data, function ($data) {
            return [
                'amount' => $data->paid,
                'payment_date_sql' => isset($data->invoice_date) ? $data->invoice_date : null,
                'client_id' => $data->client_id,
                'invoice_id' => $this->getInvoiceId($data->invoice_id),
            ];
        });
    }
}