My problem is, when customers try to use Gift Certificate they can't buy all amount. Example: Gift Certificate amount is 10€ , purhase is 20€ , customer can use only 9,99€ on Gift Certificate.

And i want also that TAX not includ Gift Certificates amount when they use it, only when customers buy Gift Certificate i want it show,but not TAX when they use it. How can i set these settings?

When customers buy Gift Certificate i want invoice it shows like this:

10.00€ Gift Certificate
1.80€ TAX
10.00€ Total amount

And when use Gift Certificate

20.00€ product xxx
5.00€ Shipping
4,51€ TAX
-10.00 Gift Certificate
15.00€ Total

can you help me set this rigt