FOX - WooCommerce Currency Switcher Professional

Plugin link: https://codecanyon.net/item/yandex-money-payment-gateway-for-woocommerce/16168016

In file \woocommerce-yandex-money.php add next code

if (class_exists('WOOCS')) {
    global $WOOCS;
    $currencies = $WOOCS->get_currencies();
    if (isset($currencies['RUB'])) {
        $rub_rate = $currencies['RUB']['rate'];
        $curr_rate = $currencies[$WOOCS->current_currency]['rate'];
        $yandex_args['sum'] = number_format(($order->order_total / $curr_rate) * $rub_rate, 2, '.', '');
    }
}