Allow WooCommerce Gateway Percentage Fee To Work Also On Order Pay

I've been using this snippet for a while with no issue until I noticed that a customer was able to pay by credit card without being charged a fee. They managed to make a payment via the "order-pay" page.

Can anyone tell me why my code isn't working on the order-pay page? It works fine on the checkout page.

// Assign Credit Card Gateway Percentage Fee to Wholesaler Profiles

add_action('woocommerce_cart_calculate_fees', 'sm_credit_card_fee_role_gateway', 10, 1);
function sm_credit_card_fee_role_gateway($cart){
    if (is_admin() && !defined('DOING_AJAX'))
        return;

    if (!(is_checkout() && !is_wc_endpoint_url()))
        return;

    if (!is_user_logged_in())
        return;

    $user = wp_get_current_user();
    $roles = (array) $user->roles;
    $roles_to_check = array('administrator', 'default_wholesaler', 'wholesaler-non-vat-registered', 'shop_manager');
    $compare = array_diff($roles, $roles_to_check);

    if (empty($compare)){
        $payment_method = WC()->session->get('chosen_payment_method');
        if ($payment_method == 'cardgatecreditcard'){
            $percentage = 0.085;
            $surcharge = (WC()->cart->cart_contents_total + WC()->cart->shipping_total) * $percentage;
            $cart->add_fee( 'Credit Card Fee (8.5%)', $surcharge, true );
        }
    }
}

To allow your code to be active on Order pay, you may replace in your code:

if ( ! ( is_checkout() && ! is_wc_endpoint_url() ) )
    return;

by:

if ( ! ( is_checkout() && ! is_wc_endpoint_url('order-received') ) )
    return;

Now your function code will also be executed on WooCommerce Order Pay endpoint…

But in Order Pay endpoint, the data is saved to an existing order, so the fee is already saved for this order when order was placed in checkout. The hook woocommerce_cart_calculate_fees affect only the cart object and doesn't have any effect on an exiting order in Order Pay endpoint.

You will have to rebuilt something much more complicated specifically for Order Pay, involving certainly Ajax, to be able to remove or add your custom fee in the existing order, refreshing totals…