Overriding Magento_SalesRule ResourceModel by preferences throws error: Type Error occurred when creating object

Error Message in debug.log:

[2020-11-10 07:57:17] main.CRITICAL: Type Error occurred when creating object: Magento\SalesRule\Model\ResourceModel\Rule, Argument 3 passed to Magento\SalesRule\Model\ResourceModel\Rule::__construct() must be an instance of Magento\SalesRule\Model\ResourceModel\Coupon, instance of RM\SameCouponMultipleDiscounts\Model\ResourceModel\Coupon given, called in /home/rehan/lab/testrm/vendor/magento/framework/ObjectManager/Factory/AbstractFactory.php on line 116 [] []

I am trying to override: Magento\SalesRule\Model\ResourceModel\Coupon.php to remove 'unique coupon' restriction:

$this->addUniqueField(['field' => 'code', 'title' => __('Coupon with the same code')]);

from construct() method.

My app/code/Vendor/Module/Model/ResourceModel/Coupon.php looks like:

<?php
/**
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */
namespace Vendor\Module\Model\ResourceModel;

use Magento\Framework\Model\AbstractModel;

/**
 * SalesRule Resource Coupon
 *
 * @author      Magento Core Team <core@magentocommerce.com>
 */
class Coupon extends \Magento\Framework\Model\ResourceModel\Db\AbstractDb implements
    \Magento\SalesRule\Model\Spi\CouponResourceInterface
{
    /**
     * Constructor adds unique fields
     *
     * @return void
     */
    protected function _construct()
    {
        $this->_init('salesrule_coupon', 'coupon_id');
    }
}

my di.xml file looks like:

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
    <preference for="Magento\SalesRule\Model\ResourceModel\Coupon" type="Vendor\Module\Model\ResourceModel\Coupon" />
</config>

I've tried clearing cache, generated folder and did setup:di:compile but I am still receiving the same error.

You should make your overridden class extends the original class so the other native classes that dependency injection original class can recognize your overridden one.

Alter

class Coupon extends \Magento\Framework\Model\ResourceModel\Db\AbstractDb implements
    \Magento\SalesRule\Model\Spi\CouponResourceInterface

into

class Coupon extends \Magento\SalesRule\Model\ResourceModel\Coupon

But using preferences aren't recommended, you can try to find a better way.