Just to let you know that's you're wrong with your 20% discount if we got all your 4 airports: after calculation the rebate is only 17.32%!!!

explanation:

22.90+3.59 (vat france)=26.49-4.58(coupon)=21.91... (20% should be 21.19)

Ehem, sorry, but your calculation is wrong (apart that the calculation is not even "our", but is done by Esellerate...)

VAT is added at the end, not before the calculation, and you just can't subtract the VAT-excluded coupon from the VAT-included amount.

So, for example, an user based in France with VAT at 19.6% will pay:

Without the Coupon:

22,90

+ 4.49 (19.6% French VAT)

-------------

27,39 Total

With the Coupon:

22,90

- 4.58 ( 20% coupon )

---------------

18,32

+ 3,59 ( 19.6% French VAT )

-------------------

21,91 in Total

and, of course, 27,39 - 20% it exactly 21,91 so you HAVE your 20% discount!

You error, is that, when making the final discount calculation, you taken into account the VAT (3,59) you have payed with the coupon, but you should have taken into account the VAT you *would have* payed if you haven't inserted the coupon, which would have been 4.49 ( 22,90+19.6%)