Pruducts with different tax rates in cart – coupons and gateaway

Dear all,

Our WC webshop is under the final stages of development. We use a gateaway to our ERP system upon checkout, so orders go through to our accounting and logistic software which creates the invoices before shipping, so it is crucial that the orders go through properly.
We have a little problem with coupons (either WC extended coupon features or Yith points and rewards) when we have products with different tax rates in the cart.

I will use the following example with the points and rewards plugin:

We have two different tax rates: regular which is 27% in hungary and reduced for books which is 5%.
I buy a book, use 100 points, get -100 HUF discount, which is -105 huf incl. VAT, all good.
I buy a card deck (regular rate), use 100 points, get -100 HUF discount, which is -127 huf incl. VAT, all good.
I buy both with one checkout the following happens: use 100 points, which is -117 huf incl. VAT, which means there gonna be a line on the invoice for:
1x webshop discount -100 huf, Vat: 17% (!) Total: -117 huf. Thing is, we cannot use the 17% VAT because theres no such thing.
Instead it should be:
1x webshop discount -50 huf, Vat: 5%, Total: -52,5 huf
1x webshop discount -50 huf, Vat: 27%, Total: -63,5 huf
This is properly displayed under orders, but it doesn’t go through like this to the gateaway.

With normal woo coupons it’s even worse.
If I use a coupon with -1000 huf, it says it’s -1160 incl. VAT in woo. But in the ERP, it’s coming through as 1000huf with a 160% VAT, resulting in a total of -2600 huf.
Instead of:
1x webshop discount -500, Vat 5%, Total: -525
1x webshop discount -500, Vat 27%, Total: -635

Hope theres a solution for this.

Thanks
K

The page I need help with: [log in to see the link]