return [
    ...

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

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',
                    ])
                ],
            ])
        ;
    }
}

namespace App\EventListener;

use BitBag\ShippingExportPlugin\Event\ExportShipmentEvent;

final class FrankMartinShippingExportEventListener
{
    public function exportShipment(ExportShipmentEvent $event): void
    {
        $shippingExport = $event->getShippingExport();
        $shippingGateway = $shippingExport->getShippingGateway();

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

        if (false) {
            $event->addErrorFlash(); // Add an error notification

            return;
        }

        $event->addSuccessFlash(); // Add success notification
        $event->saveShippingLabel("Some label content received from external API", 'pdf'); // Save label
        $event->exportShipment(); // Mark shipment as "Exported"
    }
}