How can I credit tax amounts?
If you enable the Automatically derive tax from lines option, then the amount or percentage credited to the transaction line is credited to the tax line as well. This derived tax amount is a draft calculation only.
If you want to change the derived tax, you must enter any updates at the line level. After you save or complete, the tax engine calculates the actual tax amount to be credited and updates the final tax credit amount. You can't edit the derived value after you save or complete.
If you want to credit tax only, don't enable the Automatically derive tax from lines option. Leave the Line amount blank or zero, and enter the tax percentage or amount to credit on the Tax line.