what is priority of tax?

Hi,

1. Both are used. taxA is used for the payment fees (you need to set something in either the "price" or the "percentage" settings of your payment method, otherwise, the payment fees will be 0 and the taxes on it will be 0 too). tax is used for the product price.

2. For example:
- you product costs 10€
- you configure a tax of 10%
- the product price is 10 + 1 of taxes = 11€
- you configure a payment fee of 10% with a tax of 20%
- the payment fee will be 1€ (10% of 10€) + 0.2€ of taxes
On your checkout you'll have:
- a subtotal without taxes of 10€
- a payment fee of 1€
- a 10% tax of 1€
- a 20% tax of 0.2€
- a full total of 12.20€

Hi,

3. Wasn't the example I provided in my previous message illustrating such a case ? Basically, when you need to charge a different tax rate on the payment fees than on the products, you want to be able to configure a tax category in the payment method.

4. No. If all products have the same tax just make sure you have the same tax category configured in all the products (the default tax category" is preselected when creating products, and it's also possible to run a massaction to make sure all the products have the same tax category).
Then, create a tax rate via the "manage tax rates" button of the System>Taxes menu.
And finally create a tax rule in System>Taxes to link the tax category selected in your products with the tax rate you created.
I recommend doing it that way rather than trying to use payment fees for taxes.
That way, when you go in the "manage tax rules" area in the future, you'll be able to see how much tax was paid by your customers based on the order statuses selected and based on the start/end dates selected in the filter on the top right corner of the listing, making for an easy reporting of taxes to your local tax office.