invoiceninja/app/Ninja/Intents/WebApp/CreateInvoiceIntent.php

<?php

namespace App\Ninja\Intents\WebApp;

use App\Models\Invoice;
use App\Models\EntityModel;
use App\Ninja\Intents\InvoiceIntent;
use Exception;

class CreateInvoiceIntent extends InvoiceIntent
{
    public function process()
    {
        $client = $this->requestClient();
        $clientPublicId = $client ? $client->public_id : null;

        //$invoiceItems = $this->requestInvoiceItems();

        $url = '/invoices/create/' . $clientPublicId . '?';

        foreach ($this->requestFields() as $field => $value) {
            if (in_array($field, Invoice::$requestFields)) {
                $url .= $field . '=' . urlencode($value) . '&';
            }
        }

        $url = rtrim($url, '?');
        $url = rtrim($url, '&');

        return redirect($url);
    }
}