Fixed Tax Amount on Insurance

I’m currently configuring the assurance tax on an insurance which has a fixed tax amount (amount, not percentage). I had hoped for the checkbox below to enable me to do this; however, it appears to be doing nothing. Are there any options for this?

This option lets you set the tax amount on the salesline manually. Maybe this helps you in a process to set the correct tax amount?

But the implementation can differ per application as it is a produced feature of N_Tax, so you would need to find out in the architect which fields are using this value. You can go to the Conceptmanager and select this feature. Then press the Call hierarchy button to find where it has been implemented if you know which component implements this for you. Otherwise you can open your integrated model and select the field and from there press the call hierarchy button (or right-click and select that option) to find out how your implementation works.