Field help (SQHVACBPR) 

A tax rule represents the tax territoriality principle, in other words, the calculation rules necessary to determine the amount of taxes that can be applied to the quote.

As a general rule, by crossing a tax rule linked to the BP with a Tax level, you can determine the tax code to be applied to the document line and so, to the entry line.

The tax rule is based on the tax rule of (in order of priority):

If the customer is a prospect, the default tax rule defined in the tax rule table is used.

Only a tax rule with a legislation and group that are consistent with those of the document can be entered.
SEEREFERTTO See the documentation on general principles linked to the mutli-legislation setup.

Once the quote is created, this information can no longer be modified. If however, you modify the tax rule after entering quote lines but before creating the quote, then taxes are re-calculated on all entered lines.

The parameter CTLTAX - Tax codes control (VEN chapter, VAT group) is used to control that the BP tax rule: