Not possible to apply rules

[janoschbatschi]

Whenever a rule is applied, an error is thrown:
KCO error: BAD_VALUE: Bad value: order_tax_amount (must be greater than or equal to 0)

Independent of if the rule is applied to subtotal or to each product.

This seems to be due to the cart_total being smaller than the cart_taxFreeTotal which leads to a negative value for order_tax_amount which is not allowed near

isotope-klarna-checkout/src/Module/KlarnaCheckout.php

Line 244 in c1c8109

'order_tax_amount' => (int) round(

and in the other classes where order_tax_amount is manipulated.

Example: 
	Zwischensumme		 	€ 27,00	 
 	davon Umsatzsteuer	13%	€ 3,11	 
 	Versand (Pauschalversand)	€ 10,00	 
 	Gutschein			€ -20,00	 
 	Bestellsumme		 	€ 17,00	

CartTotal: 17€ 
CartTaxFreeTotal: 37€ (27€+10€)

[janoschbatschi]

Obviously, the CartTaxFreeTotal is calculated wrong. If I use the standard Isotope checkout everything works correctly. Using KlarnaCheckout it throws the bad_value error. It seems to be depending on the shipping (taxes or not) and depending on the rules (whole cart or individual items). Once the order_tax_amount is correct but than the order_amount throws the bad value error.

For me following workaround seems to work (KlarnaCheckout.php):
'order_tax_amount' => (int) round(($this->cart->getSubTotal() - $this->cart->getTaxFreeSubTotal()) / $this->cart->getSubTotal() * ($this->cart->getTotal()-$this->cart->getShippingMethod()->price) * 100, 0),

OrderLine.php -> addTotalDiscountAmountForItem()
$this->total_discount_amount += ($surcharge->total_price * (-1));
instead of
$this->total_discount_amount += ($surcharge->getAmountForCollectionItem($this->item) * (-1));

[janoschbatschi]

The issue seems to be due to the standard tax (13%) being included in the product. For foreign customers, a different tax is added (e.g. 20%). Klarna complains because the total amount correctly has the 20% tax calculated and the product itself still has 13%. E.g. the formula Klarna checks (https://developers.klarna.com/documentation/klarna-payments/in-depth-knowledge/tax-handling/) is not correct anymore.

Another problem occurs if in the Isotope config the "Preisanzeige" is changed from "Brutto" to "Festgelegt". Then the calculation is also wrong.