Critical error when combining Tax and Coupons (and Invoice) addons - this seems to be illegal - high urgency!

I am combining the Tax, Coupons and Invoice Addons in my BookingPress instance.

There is now a critical problem concerning the calculation order of the invoice total. The calculation order seems as follows:

1. subtotal of the booked services
2. tax according to the percentage stated in the admin settings
3. coupons applied
4. total invoice

The problem with this is that taxes are declared too high if there is a granted coupon discount. The taxes are still calculated from the undiscounted subtotal.

In order to calculate the taxes correctly, one must first deduct the coupon discount from the subtotal, then apply the taxation rate on the discounted subtotal.

This bug needs a very urgent fix since all users of BookingPress might issue illegal invoices and become subject to criminal prosecution.

In many countries, the declared taxes can be reimbursed via tax return. If the declared value is too high, this poses criminal offense.

Please do fix this bug immediately. Thank you!