Need help in adding Non-taxable Service Charges

hellow, i will like to know how to add a Non-taxable Service Charges calculation.

taxes are included in my prices

ticket total: 20.000
tax total (8%): 1.481…ok
services charges (12%): 2.400…wrong…it should be 2.222

how can i calculated the service BEFORE taxes

There are several options on the calculation, sure onesne is use plain total, tried that?

this is from the first ticket screen, as far the “best” option is rate from ticket amount and check the “include tax”

with the “include tax” untick and the rate from ticket amount it get worse, withou the service charge applied the tax dfine but when i add the service it messes up the tax

with the “rate with previus template amount” and the tax included unticked does the same as the previous one.

and with the rate from previous template amount un the tax included checked is just calculate the service wrong.

and dont know…what am i not seeing? cant get ir worked. there are no more rate options in the calculation methods

cant find or see any plain total option in the calculations.