Magento 2 Custom Charge Error fixed With PayPal in Custom Module

If you want to add a custom charge to your module you can check this blog Custom Price Fee

In Magento 2 Paypal is implemented with the module name Paypal, If the customer selects the Paypal method for the payment then Magento\Paypal\Model\Cart will call instead of Magento\Payment\Model\Cart used for collecting items and amount and validate the info collected before sending to PayPal.
Now if in an order you added some custom amount, and want to pay the payment by Magento’s default PayPal payment method, then it throws the error that, the amount is not the same as the order amount.

I have described here how to solve this issue in our custom Magento2 Modules.

1) you need to create the plugin, go to NameSpace/ModuleName/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\Paypal\Model\Cart">
        <plugin name="webkul_update_paypal_custom_fee_order" type="NameSpace\ModuleName\Plugin\Model\UpdateCustomFeeForOrderPayPal"/>
    </type>
</config>

2) Now, Define this plug-in at the path NameSpace\ModuleName\Plugin\Model\UpdateCustomFeeForOrderPayPal.php

<?php
namespace NameSpace\ModuleName\Plugin\Model;
class UpdateCustomFeeForOrderPayPal
{
    /**
     * @var \Magento\Checkout\Model\Session
     */
    protected $_checkoutSession;
    const AMOUNT_SUBTOTAL = 'subtotal';
    public function __construct(
        \Magento\Checkout\Model\Session $checkoutSession
    ) {
        $this->_checkoutSession = $checkoutSession;
    }

    public function afterGetAmounts($cart,$result)
    {
        $quote = $this->_checkoutSession->getQuote();
        $paymentMethod = $quote->getPayment()->getMethod();
        $paypalMethodList = [
            'payflowpro',
            'payflow_link',
            'payflow_advanced',
            'braintree_paypal',
            'paypal_express_bml',
            'payflow_express_bml',
            'payflow_express',
            'paypal_express',
            'paypal_billing_agreement',
            'hosted_pro',
            'payflowpro_cc_vault'
        ];

        // to check the paypal payment method
        if (in_array($paymentMethod, $paypalMethodList)) {
            $result[self::AMOUNT_SUBTOTAL] = $result[self::AMOUNT_SUBTOTAL] + $quote->getCustomfee();
        }

        return $result;
    }
}

Here, we check after plugin, if you want to check how to create the plugin in Magento, You can check this blog Magento 2 Create & uses Of Plugins
Here, afterGetAmounts we check if the payment method is PayPal then we add the custom fee with the subtotal.
Hope it will help you. Thank You.