BeforeBlockToHtml.php

<?php

namespace Dotdigitalgroup\Email\Observer\Html;

/**
 * Sales rule coupon new columns (expiration_data, generated_by_dotmailer).
 */
class BeforeBlockToHtml implements \Magento\Framework\Event\ObserverInterface
{
    /**
     * @var \Dotdigitalgroup\Email\Model\Sales\CouponGridFilterer
     */
    private $couponGridFiltererFactory;

    public function __construct(
        \Dotdigitalgroup\Email\Model\Sales\CouponGridFiltererFactory $couponGridFiltererFactory
    ) {
        $this->couponGridFiltererFactory = $couponGridFiltererFactory;
    }

    /**
     * @param \Magento\Framework\Event\Observer $observer
     *
     * @return null
     */
    public function execute(\Magento\Framework\Event\Observer $observer)
    {
        $grid = $observer->getBlock();

        /**
         * \Magento\SalesRule\Block\Adminhtml\Promo\Quote\Edit\Tab\Coupons\Grid
         */
        if ($grid instanceof \Magento\SalesRule\Block\Adminhtml\Promo\Quote\Edit\Tab\Coupons\Grid) {
            $grid->addColumnAfter(
                'expiration_date',
                [
                    'header' => __('Expiration date'),
                    'index' => 'expiration_date',
                    'type' => 'datetime',
                    'default' => '',
                    'align' => 'center',
                    'width' => '160'
                ],
                'created_at'
            )->addColumnAfter(
                'generated_by_dotmailer',
                [
                    'header' => __('Generated By dotmailer'),
                    'index' => 'generated_by_dotmailer',
                    'type' => 'options',
                    'default' => '',
                    'options' => ['null' => 'No', '1' => 'Yes'],
                    'width' => '30',
                    'align' => 'center',
                    'filter_condition_callback' =>
                        [$this->couponGridFiltererFactory->create(), 'filterByGeneratedByDotmailer']
                ],
                'expiration_date'
            );
        }
    }
}