On the general ledger parameter, sales tax tab page, the parameter “Tax direction requirement” can be set = Yes.
This validation now only validates that a tax direction is entered on a main accoutn, but not the tax direction value.

If a main account has tax direction filled in as a legal entity override with value “Purchase” the validation should prevent this main account from being used on a sales order or free text invoice. The sales tax direction on sales order and free text invoice is always “Sales tax payable”, hence not in accordance with the required sales tax direction “Purchase” on the main account.

If the parameter “Tax direction requirement” only validates that a main account have a tax direction, and not validates the value, this parameter has little value for sales order and free text invoices (the validation only stop posting to main account without any sales tax directions at all).