return [
    ...

    BitBag\SyliusShippingExportPlugin\BitBagSyliusShippingExportPlugin::class => ['all' => true],
];

<?php

declare(strict_types=1);

namespace App\Form\Type;

use Symfony\Component\Form\AbstractType;
use Symfony\Component\Form\Extension\Core\Type\TextType;
use Symfony\Component\Form\FormBuilderInterface;
use Symfony\Component\Validator\Constraints\NotBlank;

final class FrankMartinShippingGatewayType extends AbstractType
{
    public function buildForm(FormBuilderInterface $builder, array $options): void
    {
        $builder
            ->add('iban', TextType::class, [
                'label' => 'IBAN',
                'constraints' => [
                    new NotBlank([
                        'message' => 'IBAN number cannot be blank.',
                        'groups' => 'bitbag',
                    ]),
                ],
            ])
            ->add('address', TextType::class, [
                'label' => 'Address',
                'constraints' => [
                    new NotBlank([
                        'message' => 'Address cannot be blank.',
                        'groups' => 'bitbag',
                    ]),
                ],
            ])
        ;
    }
}

<?php

declare(strict_types=1);

namespace App\EventListener;

use BitBag\SyliusShippingExportPlugin\Entity\ShippingExportInterface;
use Doctrine\Persistence\ObjectManager;
use Sylius\Bundle\ResourceBundle\Event\ResourceControllerEvent;
use Symfony\Component\Filesystem\Filesystem;
use Symfony\Component\HttpFoundation\RequestStack;
use Webmozart\Assert\Assert;

final class FrankMartinShippingExportEventListener
{
    /** @var RequestStack */
    private $requestStack;

    /** @var Filesystem */
    private $filesystem;

    /** @var ObjectManager */
    private $shippingExportManager;

    /** @var string */
    private $shippingLabelsPath;

    public function __construct(
        RequestStack $requestStack,
        Filesystem $filesystem,
        ObjectManager $shippingExportManager,
        string $shippingLabelsPath
    ) {
        $this->requestStack = $requestStack;
        $this->filesystem = $filesystem;
        $this->shippingExportManager = $shippingExportManager;
        $this->shippingLabelsPath = $shippingLabelsPath;
    }

    public function exportShipment(ResourceControllerEvent $event): void
    {
        /** @var ShippingExportInterface $shippingExport */
        $shippingExport = $event->getSubject();
        Assert::isInstanceOf($shippingExport, ShippingExportInterface::class);

        $shippingGateway = $shippingExport->getShippingGateway();
        Assert::notNull($shippingGateway);

        if ('frank_martin_shipping_gateway' !== $shippingGateway->getCode()) {
            return;
        }

        $session = $this->requestStack->getSession();
        $flashBag = $session->getBag('flashes');

        if (false) {
            $flashBag->add('error', 'bitbag.ui.shipping_export_error'); // Add an error notification

            return;
        }

        $flashBag->add('success', 'bitbag.ui.shipment_data_has_been_exported'); // Add success notification
        $this->saveShippingLabel($shippingExport, 'Some label content received from external API', 'pdf'); // Save label
        $this->markShipmentAsExported($shippingExport); // Mark shipment as "Exported"
    }

    public function saveShippingLabel(
        ShippingExportInterface $shippingExport,
        string $labelContent,
        string $labelExtension
    ): void {
        $labelPath = $this->shippingLabelsPath
            . '/' . $this->getFilename($shippingExport)
            . '.' . $labelExtension;

        $this->filesystem->dumpFile($labelPath, $labelContent);
        $shippingExport->setLabelPath($labelPath);

        $this->shippingExportManager->persist($shippingExport);
        $this->shippingExportManager->flush();
    }

    private function getFilename(ShippingExportInterface $shippingExport): string
    {
        $shipment = $shippingExport->getShipment();
        Assert::notNull($shipment);

        $order = $shipment->getOrder();
        Assert::notNull($order);

        $orderNumber = $order->getNumber();

        $shipmentId = $shipment->getId();

        return implode(
            '_',
            [
                $shipmentId,
                preg_replace('~[^A-Za-z0-9]~', '', $orderNumber),
            ]
        );
    }

    private function markShipmentAsExported(ShippingExportInterface $shippingExport): void
    {
        $shippingExport->setState(ShippingExportInterface::STATE_EXPORTED);
        $shippingExport->setExportedAt(new \DateTime());

        $this->shippingExportManager->persist($shippingExport);
        $this->shippingExportManager->flush();
    }
}