QuoteBackendValidationRule

CustomValidationRule.php

<?php

declare(strict_types=1);

namespace MageVision\Blog80\Model\Quote\ValidationRule;

use Magento\Framework\Validation\ValidationResultFactory;
use Magento\Quote\Model\Quote;
use Magento\Quote\Model\ValidationRules\QuoteValidationRuleInterface;

class CustomValidationRule implements QuoteValidationRuleInterface
{
    /**
     * @var ValidationResultFactory
     */
    private $validationResultFactory;

    /**
     * @param ValidationResultFactory $validationResultFactory
     */
    public function __construct(
        ValidationResultFactory $validationResultFactory,
    ) {
        $this->validationResultFactory = $validationResultFactory;
    }

    /**
     * @inheritdoc
     *
     * @param Quote $quote
     * @return array
     */
    public function validate(Quote $quote): array
    {
        $validationErrors = [];

        if ($quote->isVirtual()) {
            $validationErrors[] = __(
                'Quote is Virtual!'
            );
        }

        return [$this->validationResultFactory->create(['errors' => $validationErrors])];
    }
}

di.xml

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
    <type name="Magento\Quote\Model\ValidationRules\QuoteValidationComposite">
        <arguments>
            <argument name="validationRules" xsi:type="array">
                <item name="CustomValidationRule" xsi:type="object">MageVision\Blog80\Model\Quote\ValidationRule\CustomValidationRule</item>
            </argument>
        </arguments>
    </type>
</config>