Magento 2 apply discount on tax issue + FPT

Question

Firstly I am using Magento 2.1.8 version

I'm facing an issue with tax total amount and discount from coupon code. Whenever I apply a discount coupon on cart, tax amount stays the same. I have read a few posts saying that Magento 2 option:

My options:
Catalog Prices: Excluding tax
Apply Customer Tax: After discount
Apply Discount On Prices: Exclude tax

Moreover product have FTP (Fixed product taxes) set.

Maybe someone know this issue and have a fix for it? Also it would be great if someone could confirm that they also facing the same issue (add discount - tax stays the same, using FPT)

Thanks for any help

Answer 1

After some more research and discussions, we got a conclusion. Apparently FPT (fixed product tax) meant to be Fixed and it doesn't change dynamically. Changing it dynamically would break it's logic. If someone disagrees - please write you own opinion to the comments below.

I have checked it with the product without FPT, only with simple tax class, taxes were changing as discount was applied.

If you still know how to apply a discount on FPT product taxes, please share your knowledge, there might be people who still need to do it (sometimes clients can be demanding).