magento2: Multi-Currency not working when setting Custom Prices on adding product to Cart. This occurs on version 2.4.2 and previous versions as well

[Magento Version 2.4.6]

I faced the same issue while using the above code to add a custom price. I found there is one file where the getCustomPrice() function is called but it is not implemented that’s why we did not get the proper custom price.

Path: /vendor/magento/module-quote/Model/Quote/Item.php

After I solved addtocart event issue there was one more problem because of the currency switcher. I checked the quote_item table and found a difference between normal and custom price values. I created a plugin for it and fixed that issue.

Path: vendor/magento/module-directory/Controller/Currency/SwitchAction.php

I added the whole solution here.

app/code/Msquare/ModuleName/etc/frontend

events.xml

<?xml version="1.0"?>
<!--
/**
 * @category Msquare
 * @package Msquare_CustomPriceFix
 * @author Mahesh Makwana <maheshmakwana588@gmail.com>
 */
-->
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Event/etc/events.xsd">
    <event name="checkout_cart_product_add_after">
        <observer name="custom_price_add" instance="Msquare\CustomPriceFix\Observer\CustomPrice" />
    </event>
</config>

app/code/Msquare/ModuleName/Observer

CustomPrice.php

<?php
/**
 * @category Msquare
 * @package Msquare_CustomPriceFix
 * @author Mahesh Makwana <maheshmakwana588@gmail.com>
 */
namespace Msquare\CustomPriceFix\Observer;

use Msquare\CustomPriceFix\Helper\Data as DataHelper;
use Magento\Framework\Currency\Data\Currency as CurrencyData;
use Magento\Framework\Event\Observer;
use Magento\Framework\Event\ObserverInterface;

class CustomPrice implements ObserverInterface
{
    /**
     * @param DataHelper $dataHelper
     */
    public function __construct(
        protected DataHelper $dataHelper
    ) {}

    public function execute(Observer $observer)
    {
        $item = $observer->getEvent()->getData('quote_item');
        $item = ($item->getParentItem() ? $item->getParentItem() : $item);
        $price = 100; //set your price here

        $curentCurrency = $this->dataHelper->getCurrentCurrency();
        $baseCurrency = $this->dataHelper->getBaseCurrency();
        if ($curentCurrency != $baseCurrency) {
            $currencyObj = $this->dataHelper->getCurrencyFactory();
            $rate = $currencyObj->load($baseCurrency)->getAnyRate($curentCurrency);
            $price *= $rate;
            $price = (float) $currencyObj->format($price, ['display' => CurrencyData::NO_SYMBOL], false);
        }

        $item->setCustomPrice($price);
        $item->setOriginalCustomPrice($price);
        $item->getProduct()->setIsSuperMode(true);
    }

}

app/code/Msquare/ModuleName/Helper

Data.php

<?php
/**
 * @category Msquare
 * @package Msquare_CustomPriceFix
 * @author Mahesh Makwana <maheshmakwana588@gmail.com>
 */
namespace Msquare\CustomPriceFix\Helper;

use Magento\Checkout\Model\CartFactory;
use Magento\Directory\Model\CurrencyFactory;
use Magento\Store\Model\StoreManagerInterface;

class Data
{
    public function __construct(
        protected StoreManagerInterface $storeManager,
        protected CurrencyFactory $currencyFactory,
        protected CartFactory $cartFactory
    ) {}

    /**
     * Get base currency code
     *
     * @return string
     */
    public function getBaseCurrency()
    {
        return $this->storeManager->getStore()->getBaseCurrency()->getCurrencyCode();
    }

    /**
     * Get current currency code
     *
     * @return string
     */
    public function getCurrentCurrency()
    {
        return $this->storeManager->getStore()->getCurrentCurrency()->getCurrencyCode();
    }

    /**
     * Get currency factory
     *
     * @return CurrencyFactory
     */
    public function getCurrencyFactory()
    {
        return $this->currencyFactory->create();
    }

    /**
     * Get cart items
     *
     * @return CartFactory
     */
    public function getCartItems()
    {
        return $this->cartFactory->create()->getQuote()->getAllItems();
    }

}

app/code/Msquare/ModuleName/etc/frontend

di.xml

<?xml version="1.0"?>
<!--
/**
 * @category Msquare
 * @package Msquare_CustomPriceFix
 * @author Mahesh Makwana <maheshmakwana588@gmail.com>
 */
-->
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
    <type name="Magento\Directory\Controller\Currency\SwitchAction">
        <plugin name="custom_price_fix"
                type="Msquare\CustomPriceFix\Plugin\Direcotry\Controller\Currency\SwitchAction"
                sortOrder="10"/>
    </type>
</config>

app/code/Msquare/ModuleName/Plugin/Direcotry/Controller/Currency

SwitchAction.php

<?php
/**
 * @category Msquare
 * @package Msquare_CustomPriceFix
 * @author Mahesh Makwana <maheshmakwana588@gmail.com>
 */
namespace Msquare\CustomPriceFix\Plugin\Direcotry\Controller\Currency;

use Msquare\CustomPriceFix\Helper\Data as DataHelper;
use Magento\Directory\Controller\Currency\SwitchAction as SwitchActionParent;
use Magento\Framework\Currency\Data\Currency as CurrencyData;

class SwitchAction
{
    /**
     * @param DataHelper $dataHelper
     */
    public function __construct(
        protected DataHelper $dataHelper
    ) {}

    /**
     * Currency switcher before plugin
     *
     * @param SwitchActionParent $subject
     *
     * @return void
     */
    public function beforeExecute(SwitchActionParent $subject)
    {
        $items = $this->dataHelper->getCartItems();
        $currencyObj = $this->dataHelper->getCurrencyFactory();
        $baseCurrency = $this->dataHelper->getBaseCurrency();
        $newCurrency = (string) $subject->getRequest()->getParam('currency');
        if ($newCurrency != $baseCurrency) {
            /* Update Price for Other Currency */
            $rate = $currencyObj->load($baseCurrency)->getAnyRate($newCurrency);
            foreach ($items as $item) {
                $customPrice = $item->getBasePrice();
                $customPrice *= $rate;
                $customPrice = (float) $currencyObj->format($customPrice, ['display' => CurrencyData::NO_SYMBOL], false);
                $item->setCustomPrice($customPrice);
                $item->setOriginalCustomPrice($customPrice);
                $item->getProduct()->setIsSuperMode(true);
                $item->save();
            }

        } else {
            /* Update Price for Base Currency */
            foreach ($items as $item) {
                $item->setCustomPrice($item->getBasePrice());
                $item->setOriginalCustomPrice($item->getBasePrice());
                $item->getProduct()->setIsSuperMode(true);
                $item->save();
            }
        }
    }
}

Note: Here NO_SYMBOL constant value is 1. You can also add static value. Path: vendor/magento/framework/Currency/Data/Currency.php