Sometime we need to have a condition to enable or disable COD (cash on delivery payment). In my case my client asked me COD should be enable just for some regions.

Now i want to share my code and my solution .

Create this file or if it exist just add the code app/code/Darvishani/COD/etc/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\OfflinePayments\Model\Cashondelivery">
        <plugin name="cashondeliveryplugforregion"
                type="Darvishani\COD\Plugin\CashondeliveryPlug"
                disabled="false" sortOrder="10"/>
    </type>
</config>

Now you need to add a class app/code/Darvishani/COD/Plugin/CashondeliveryPlug.php

<?php

namespace Darvishani\COD\Plugin;

use Magento\Checkout\Model\Session;
use Magento\Payment\Model\Method\AbstractMethod;
use Magento\Quote\Model\Quote;
use Psr\Log\LoggerInterface;

class CashondeliveryPlug
{

    /**
     * @var Session
     */
    protected $_checkoutSession;

    /**
     * Constructor
     *
     * @param Session $checkoutSession
     */
    public function __construct(
        LoggerInterface $logger,
        Session $checkoutSession
    ) {
        $this->logger = $logger;
        $this->_checkoutSession = $checkoutSession;
    }

    public function aroundIsAvailable(
        \Magento\Payment\Model\Method\AbstractMethod $subject, callable $proceed)
    {
        $shippingAddress = $this->_checkoutSession->getQuote()->getShippingAddress();
        $currentRegionCode=$shippingAddress->getRegionId();
    
        $enableRegion=['7','25'];
        if(is_array($enableRegion) && in_array($currentRegionCode,$enableRegion)){
            return  true;
        }else{
            return  false;
        }

        return $proceed();
    }
}

You need to compile your code and clear Magento cache