Hello,
I need to add a coupon programmatically to already exsiting order. It works very well with creating new order via new Cart() and same named method addCartRule(). But when I try to add a coupon to an existing order (1) it's being created in all coupons, (2) it's even added to an order, but unfortunately: (3) the discount does not affect the invoice and total amount, (4) it disappears when I update this specific order discounts through BO (f.e. want to add another coupon or delete existing one).
For creating throught new Cart i use following code:
// Create New Cart
$new_cart = new Cart();
$new_cart->id_lang = (int) $orderData['id_lang'];
$new_cart->id_shop = (int) $orderData['id_shop'];
$new_cart->id_shop_group = (int) $orderData['id_shop_group'];
$new_cart->id_currency = $orderData['id_currency'];
$new_cart->id_customer = $orderData['id_customer'];
$new_cart->id_address_delivery = $orderData['id_address_delivery'];
$new_cart->id_address_invoice = $orderData['id_address_invoice'];
$new_cart->id_carrier = $orderData['id_carrier'];
$new_cart->add();
// Create Cart Rule - discount 100%
$cart_rule = new CartRule();
$cart_rule->id_customer = $new_cart->id_customer;
$cart_rule->name = array(
Configuration::get('PS_LANG_DEFAULT') => $this->l('Discount 100%')
);
$cart_rule->date_from = date('Y-m-d H:i:s', time());
$cart_rule->date_to = date('Y-m-d H:i:s', time() + 24 * 3600);
$cart_rule->code = $this->customGenerateCouponCode();
$cart_rule->quantity = 1;
$cart_rule->quantity_per_user = 1;
$cart_rule->minimum_amount_currency = $new_cart->id_currency;
$cart_rule->reduction_currency = $new_cart->id_currency;
$cart_rule->free_shipping = true;
$cart_rule->reduction_percent = 100;
$cart_rule->active = 1;
$cart_rule->add();
// Add cart rule to cart and in order
$values = array(
'tax_incl' => $cart_rule->getContextualValue(true),
'tax_excl' => $cart_rule->getContextualValue(false)
);
$new_cart->addCartRule($cart_rule->id, $cart_rule->name[Configuration::get('PS_LANG_DEFAULT')], $values);
// Creating order from cart
$payment_module = Module::getInstanceByName('ps_wirepayment');
$resultp = $payment_module->validateOrder(
$new_cart->id,
35,
$new_cart->getOrderTotal(),
$orderData['payment_title'],
$orderData['comment'],
[],
null,
false,
$orderData['secure_key']
);
And it works well. Below there is code to add coupon to existing order, and I have problem with the invoice.
$order = new Order((int) $orderData['id_order']);
$discountAmount = $this->customGetDiscountAmmount($orderData);
// Create Cart Rule
$cart_rule = new CartRule();
$cart_rule->id_customer = $orderData['id_customer'];
$cart_rule->name = array(
Configuration::get('PS_LANG_DEFAULT') => $this->l('Discount amount: ') . $discountAmount['tax_incl']
);
$cart_rule->date_from = date('Y-m-d H:i:s', time());
$cart_rule->date_to = date('Y-m-d H:i:s', time() + 24 * 3600);
$cart_rule->code = $this->customGenerateCouponCode();
$cart_rule->quantity = 1;
$cart_rule->quantity_per_user = 1;
$cart_rule->minimum_amount_currency = $orderData['id_currency'];
$cart_rule->reduction_currency = $orderData['id_currency'];
$cart_rule->free_shipping = false;
$cart_rule->partial_use = 0;
$cart_rule->reduction_amount = (int) $discountAmount['tax_incl']; #discount value
$cart_rule->active = 1;
$cart_rule->add();
// Add cart rule to cart and in order
$values = array(
'tax_incl' => (int) $discountAmount['tax_incl'],
'tax_excl' => (int) $discountAmount['tax_excl']
);
$order->addCartRule($cart_rule->id, $cart_rule->name[Configuration::get('PS_LANG_DEFAULT')], $values, $orderData['invoice_number']);
The discount is visible in order details, but doesn't affect the total price. 
ps_order_cart_rules
ps_orders:
ps_order_invoice:
BO>Catalog>Coupons:
Adding new coupon from BO to this order unbinds all coupons added through $order->addCartRule() method to this order.
How to add coupon properly to existing order and how to make it affect order total amount?
Thanks in advance!