WooCommerce Checkout Add-Ons (by WooCommerce)
Plugin link: https://woocommerce.com/products/woocommerce-checkout-add-ons/
To your current child wp theme file functions.php add next code:
function wc_checkout_add_ons_woocs_currency_support($cost) { return apply_filters('woocs_exchange_value', $cost); } add_filter('wc_checkout_add_ons_add_on_option_cost', 'wc_checkout_add_ons_woocs_currency_support', 100); add_filter('woocommerce_checkout_add_on_get_adjustment', 'wc_checkout_add_ons_woocs_currency_support', 100);